5,893 research outputs found
The value of performance weights and discussion in aggregated expert judgements
In risky situations characterized by imminent decisions, scarce resources, and insufficient data, policymakers rely on experts to estimate model parameters and their associated uncertainties. Different elicitation and aggregation methods can vary substantially in their efficacy and robustness. While it is generally agreed that biases in expert judgments can be mitigated using structured elicitations involving groups rather than individuals, there is still some disagreement about how to best elicit and aggregate judgments. This mostly concerns the merits of using performanceâbased weighting schemes to combine judgments of different individuals (rather than assigning equal weights to individual experts), and the way that interaction between experts should be handled. This article aims to contribute to, and complement, the ongoing discussion on these topics
Management and visualization of spatiotemporal information in GIS
Although Geographic Information Systems (GIS) have been recognised as the most
advanced technology for the management of geospatial information, they are still
unable to efficiently manage the temporal dimension. Originally this problem affeeted only the study and analysis of highly dynamic phenomena. Today's expansion of GIS technology, the ease to acquire and store geospatial data and the increased capacity of computing technologies to managc large amounl of data have contributed lo the propagation of this problem across the whole geospatial seclor.
The extended use of GIS in decision-making processes is increasing the demand for
tools able to manage and 10 analyse dynamic geospatial phenomena where the
temporal dimension is crucial. The only temporal model available in commercial
GIS packages is based on discretisation of temporal data. Changes are represented as
a succession of snapshots. The dynamics and what happens between those stages are
not registered. In addition, this approach presents severe problems due to
unavoidable multiplication of data volume, abundant redundancies, loss in query
efficiency and the impossibility of knowing when the exact timing of changes occurs.
Since the late 1980s and particularly in the 1990s, researching the temporal changes
and the conceptual and technological options available has been undertaken by the
GIS and DBMS sectors. The primary objective of the research presented in this
paper is the development of a model for the integration of temporal data with GIS.
The method adopted to achieve this objective is based on the combination of Time
Geography principies, its graphic language and dynamic segmentation techniques
used in GIS. Past research has demonstrated that the difficulty to integrate time with
GIS has its origin in the continuous nature of time. Dynamic segmentation in GIS
network analysis has the potential to provide the means for a time-GIS integration in a continuous manner. Lifelines, one of the main Time geography's graphic language
elements, has been modelled as a set of network segments where the dynamics in
attribute information has been attached to different time segments rather than
distance segments (for exampIe Euclidean or cost-based) as normally occurs in
dynamic segmentation. This paper summarises initial findings of the project. These
outcomes have the potential to improve the way the geospatial sector currently
handles temporal information. However, the static nature of current GIS technology
impedes an appropriate visualisation of dynamic temporal phenomena. To this
effect, the paper also explores the possibilities offered by multimedia techniques as a complement to GIS capabilities
Dark Matter Halo Growth II: Diffuse Accretion and its Environmental Dependence
Dark matter haloes in Lambda CDM simulations grow by mergers with other
haloes as well as accretion of "diffuse" non-halo material. We quantify the
mass growth rates via these two processes, dM_mer/dt and dM_dif/dt, and their
dependence on halo environment using the ~500,000 haloes in the Millennium
simulation. Adopting a local mass density parameter as a measure of halo
environment, we find the two rates show strong but opposite environmental
dependence, with mergers playing an increasingly important role for halo
growths in overdense regions and diffuse accretion dominating growth in voids.
This behaviour is independent of the mass cuts used to define haloes vs
non-haloes. For galaxy-scale haloes, these two opposite correlations largely
cancel out, but a weak environmental dependence remains that results in a
slightly lower mean total growth rate, and hence an earlier mean formation
redshift, for haloes in denser regions. The mean formation redshift of the
~5000 cluster-mass haloes, on the other hand, appears to have no correlation
with halo environment. The origin of the positive correlation of dM_mer/dt with
local density can be traced to the surrounding mass reservoir outside the
haloes, where more progenitor haloes are available in denser regions. The
negative correlation of dM_dif/dt with density, however, is not explained by
the available diffuse mass in the reservoir, which is in fact larger in denser
regions. The non-halo component may therefore be partially comprised of truly
diffuse dark matter particles that are dynamically hotter and are accreted at a
suppressed rate in denser regions. We also discuss the implications of these
results for how to modify the Extended Press-Schechter model of halo growth,
which in its original form does not predict environmental dependence.Comment: 15 pages, 9 figures, accepted in MNRA
The Merger Rates and Mass Assembly Histories of Dark Matter Haloes in the Two Millennium Simulations
We construct merger trees of dark matter haloes and quantify their merger
rates and mass growth rates using the joint dataset from the Millennium and
Millennium-II simulations. The finer resolution of the Millennium-II Simulation
has allowed us to extend our earlier analysis of halo merger statistics to an
unprecedentedly wide range of descendant halo mass (10^10 < M0 < 10^15 Msun),
progenitor mass ratio (10^-5 < xi < 1), and redshift (0 < z < 15). We update
our earlier fitting form for the mean merger rate per halo as a function of
M_0, xi, and z. The overall behavior of this quantity is unchanged: the rate
per unit redshift is nearly independent of z out to z~15; the dependence on
halo mass is weak (M0^0.13); and it is nearly a power law in the progenitor
mass ratio (xi^-2). We also present a simple and accurate fitting formula for
the mean mass growth rate of haloes as a function of mass and redshift. This
mean rate is 46 Msun/yr for 10^12 Msun haloes at z=0, and it increases with
mass as M^{1.1} and with redshift as (1+z)^2.5 (for z > 1). When the fit for
the mean mass growth rate is integrated over a halo's history, we find
excellent match to the mean mass assembly histories of the simulated haloes. By
combining merger rates and mass assembly histories, we present results for the
number of mergers over a halo's history and the statistics of the redshift of
the last major merger.Comment: 12 pages, 9 figures, accepted in MNRA
On the fairness of the main galaxy sample of SDSS
Flux-limited and volume-limited galaxy samples are constructed from SDSS data
releases DR4, DR6 and DR7 for statistical analysis. The two-point correlation
functions , monopole of three-point correlation functions ,
projected two-point correlation function and pairwise velocity dispersion
are measured to test if galaxy samples are fair for these
statistics. We find that with increment of sky coverage of SDSS, of
flux-limited sample is extremely robust and insensitive to local structures at
low redshift. But for volume-limited samples fainter than at large scales
s>\sim 10\hmpc, deviation of and of DR7 to those of DR4
and DR6 increases with larger absolute magnitude. In the weakly nonlinear
regime, there is no agreement between of different data releases in
all luminosity bins. Furthermore, of volume-limited samples of DR7 in
luminosity bins fainter than are significantly larger,
and of the two faintest volume-limited samples of DR7 display
very different scale dependence than results of DR4 and DR6. Our findings call
for cautions in understanding clustering analysis results of SDSS faint galaxy
samples, and higher order statistics of SDSS volume-limited samples in the
weakly nonlinear regime. The first zero-crossing points of of
volume-limited samples are also investigated and discussed.Comment: 16 pages, 12 figures, accepte
Improving Correlation Function Fitting with Ridge Regression: Application to Cross-Correlation Reconstruction
Cross-correlation techniques provide a promising avenue for calibrating
photometric redshifts and determining redshift distributions using spectroscopy
which is systematically incomplete (e.g., current deep spectroscopic surveys
fail to obtain secure redshifts for 30-50% or more of the galaxies targeted).
In this paper we improve on the redshift distribution reconstruction methods
presented in Matthews & Newman (2010) by incorporating full covariance
information into our correlation function fits. Correlation function
measurements are strongly covariant between angular or spatial bins, and
accounting for this in fitting can yield substantial reduction in errors.
However, frequently the covariance matrices used in these calculations are
determined from a relatively small set (dozens rather than hundreds) of
subsamples or mock catalogs, resulting in noisy covariance matrices whose
inversion is ill-conditioned and numerically unstable. We present here a method
of conditioning the covariance matrix known as ridge regression which results
in a more well behaved inversion than other techniques common in large-scale
structure studies. We demonstrate that ridge regression significantly improves
the determination of correlation function parameters. We then apply these
improved techniques to the problem of reconstructing redshift distributions. By
incorporating full covariance information, applying ridge regression, and
changing the weighting of fields in obtaining average correlation functions, we
obtain reductions in the mean redshift distribution reconstruction error of as
much as ~40% compared to previous methods. In an appendix, we provide a
description of POWERFIT, an IDL code for performing power-law fits to
correlation functions with ridge regression conditioning that we are making
publicly available.Comment: 10 pages, 6 figure
A redshift distortion free correlation function at third order in the nonlinear regime
The zeroth-order component of the cosine expansion of the projected
three-point correlation function is proposed for clustering analysis of cosmic
large scale structure. These functions are third order statistics but can be
measured similarly to the projected two-point correlations. Numerical
experiments with N-body simulations indicate that the advocated statistics are
redshift distortion free within 10% in the non-linear regime on scales
~0.2-10Mpc/h. Halo model prediction of the zeroth-order component of the
projected three-point correlation function agrees with simulations within ~10%.
This lays the ground work for using these functions to perform joint analyses
with the projected two-point correlation functions, exploring galaxy clustering
properties in the framework of the halo model and relevant extensions.Comment: 10 pages, 6 figs; MNRAS accepte
Advancing the Transition to a High Performance Rural Health System
There are growing concerns about the current and future state of rural health. Despite decades of policy efforts to stabilize rural health systems through a range of policies and loan and grant programs, accelerating rural hospital closures combined with rapid changes in private and public payment strategies have created widespread concern that these solutions are inadequate for addressing current rural health challenges. The rural health system of today is the product of legacy policies and programs that often do not âfitâ current local needs. Misaligned incentives undermine high-value and efficient care delivery. While there are limitations related to scalability in rural health system development, rural communities do have enormous potential to achieve the objectives of a high performance rural health system. This brief (and a companion paper at http://www.rupri.org/areas-of-work/health-policy/) discusses strategies and options for creating a pathway to a transformed, high performing rural health system
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Impact of the earthworm Lumbricus terrestris (L.) on As, Cu, Pb and Zn mobility and speciation in contaminated soils
To assess the risks that contaminated soils pose to the environment properly a greater understanding of how soil biota influence the mobility of metal(loid)s in soils is required. Lumbricus terrestris L. were incubated in three soils contaminated with As, Cu, Pb and Zn. The concentration and speciation of metal(loid)s in pore waters and the mobility and partitioning in casts were compared with earthworm-free soil. Generally the concentrations of water extractable metal(loid)s in earthworm casts were greater than in earthworm-free soil. The impact of the earthworms on concentration and speciation in pore waters was soil and metal specific and could be explained either by earthworm induced changes in soil pH or soluble organic carbon. The mobilisation of metal(loid)s in the environment by earthworm activity may allow for leaching or uptake into biota
Factors associated with crisis pregnancies in Ireland: Findings from three nationally representative sexual health surveys
Background: Findings on the demographic and sexual health characteristics associated with the experience of a crisis pregnancy is important to inform the public health policy of a country, including Ireland. Findings from other jurisdictions have suggested that certain demographic groups are at risk for unintended pregnancies and the disparity between the groups have been growing in recent years. Ireland is a country which experienced much economic and societal change in the first decade of the 21st century, changes which are likely to have affected demographic variables pertaining to sexual health. The current study had two aims: to investigate changes in the socioeconomic characteristics associated with crisis pregnancies over a seven year period [2003 to 2010], and to investigate the recent [2010] socioeconomic risk factors associated with crisis pregnancies in Ireland.
Methods: The study compared the results from 18-45 year old women using data from three broadly similar nationally representative Irish sexual health surveys carried out in 2003, 2004-2006 and 2010. Chi square analysis compared of the socioeconomic characteristics across the seven year period and found that a higher proportion of women with two or more children and women for whom religion was not important reported a crisis pregnancy in 2010 compared with earlier years. A logistic regression then investigated the sexual health history and socioeconomic factors associated with the experience of a recent crisis pregnancy using the most recent 2010 data.
Results: Receipt of sex education and contraception use at first sex significantly predicted the experiencing of a recent crisis pregnancy. Younger women and those with a lower level of education were more likely to report having experienced a recent crisis pregnancy.
Conclusion: Similar demographic groups are at risk for experiencing a crisis pregnancy in Ireland compared with international research, yet the disparities between demographic groups who have experienced a crisis pregnancy appear to be decreasing rather than increasing over a seven year period. Recommendations are made with regard to the provision of continued sex education throughout the lifespan, particularly for those women who are at an increased risk of experiencing a crisis pregnancy
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