5,089 research outputs found
The Formation of a Bound Star Cluster: From the Orion Nebula Cluster to the Pleiades
(shortened) Direct N-body calculations are presented of the formation of
Galactic clusters using GasEx, which is a variant of the code Nbody6. The
calculations focus on the possible evolution of the Orion Nebula Cluster (ONC)
by assuming that the embedded OB stars explosively drove out 2/3 of its mass in
the form of gas about 0.4 Myr ago. A bound cluster forms readily and survives
for 150 Myr despite additional mass loss from the large number of massive
stars, and the Galactic tidal field. This is the very first time that cluster
formation is obtained under such realistic conditions. The cluster contains
about 1/3 of the initial 10^4 stars, and resembles the Pleiades Cluster to a
remarkable degree, implying that an ONC-like cluster may have been a precursor
of the Pleiades. This scenario predicts the present expansion velocity of the
ONC, which will be measurable by upcoming astrometric space missions (DIVA and
GAIA). These missions should also detect the original Pleiades members as an
associated expanding young Galactic-field sub-population. The results arrived
at here suggest that Galactic clusters form as the nuclei of expanding OB
associations.Comment: MNRAS, in press, 36 pages, 15 figures; repl.vers. contains
adjustments for consistency with published versio
Nature of fault planes in solid neutron star matter
The properties of tectonic earthquake sources are compared with those deduced
here for fault planes in solid neutron-star matter. The conclusion that
neutron-star matter cannot exhibit brittle fracture at any temperature or
magnetic field is significant for current theories of pulsar glitches, and of
the anomalous X-ray pulsars and soft-gamma repeaters.Comment: 5 AAS LaTeX pages 1 eps figur
ESTIMATING WILLINGNESS-TO-PAY USING A POLYCHOTOMOUS CHOICE FUNCTION: AN APPLICATION TO PORK PRODUCTS WITH ENVIRONMENTAL ATTRIBUTES
This paper utilizes a polychotomous choice function to investigate the relationship between socioeconomic characteristics and willingness-to-pay for embedded environmental attributes. Specifically, a two-stage estimation procedure with an ordered probit selection rule is used to predict the premium payers and the magnitude of the premium they are willing to pay.Research Methods/ Statistical Methods,
Web learning in post registration nurse education: application and theory. A practical experience of combining humanistic, educational and technological considerations
As healthcare becomes more knowledge intensive, nurses are challenged to effectively manage clinical information and keep abreast of professional knowledge (Procter 2001; Snyder - Halpern et al 2001; Pare & Elam 1998). Rapid
proliferation of new knowledge, expanding professional practice expectations and changing practice environments require that nurses become lifelong learners capable of constantly reflecting on and modifying their practice. Nurse education needs to embrace and make use of information
technology learning media to help nurses meet these demands. This paper considers how post registration nursing students responded to a technology based learning package directed at enhancing mental health skills and care management. At the completion of the course the participants completed a module evaluation. Representative participants comments are presented throughout this paper to highlight issues raised within the literature on technology based learning
Estimating Willingness to Pay Using a Polychotomous Choice Function: An Application to Pork Products with Environmental Attributes
Bid data from a Vickrey auction for pork chops with embedded environmental attributes were analyzed. It was found that approximately 62% of the participants had a positive WTP for the most "environmentally friendly" package of pork. Thirty percent of the participants had no WTP, and 8% had a negative WTP. A polychotomous choice model was used to accommodate data having an anchoring point within the distribution of the data. Standard variables found in the WTP literature coupled with this model were used to predict participants who were premium payers and non-premium payers using an estimated ordered probit equation.anchoring points, environmental attributes, ordered probit, polychotomous choice functions, pork, Vickrey auction, willingness to pay, Consumer/Household Economics, Demand and Price Analysis,
Data management study, volume 5. Appendix J - Contractor data package procurement and contracting /PC/ Final report
Contractor data package for administration of procurement and contracting of Voyager spacecraft system
Chandra Observations of the Optically Dark GRB030528
The X-ray-rich GRB030528 was detected by the HETE satellite and its
localization was rapidly disseminated. However, early optical observations
failed to detect a counterpart source. In a 2-epoch ToO observation with
Chandra, we discovered a fading X-ray source likely counterpart to GRB030528.
The source brightness was typical of X-ray afterglows observed at similar
epochs. Other observers detected an IR source at a location consistent with the
X-ray source. The X-ray spectrum is not consistent with a large absorbing
column.Comment: 4 pages, 1 figures, to appear in Santa Fe GRB Conference Proceedings,
200
De-blending Deep Herschel Surveys: A Multi-wavelength Approach
Cosmological surveys in the far infrared are known to suffer from confusion.
The Bayesian de-blending tool, XID+, currently provides one of the best ways to
de-confuse deep Herschel SPIRE images, using a flat flux density prior. This
work is to demonstrate that existing multi-wavelength data sets can be
exploited to improve XID+ by providing an informed prior, resulting in more
accurate and precise extracted flux densities. Photometric data for galaxies in
the COSMOS field were used to constrain spectral energy distributions (SEDs)
using the fitting tool CIGALE. These SEDs were used to create Gaussian prior
estimates in the SPIRE bands for XID+. The multi-wavelength photometry and the
extracted SPIRE flux densities were run through CIGALE again to allow us to
compare the performance of the two priors. Inferred ALMA flux densities
(F), at 870m and 1250m, from the best fitting SEDs from the
second CIGALE run were compared with measured ALMA flux densities (F) as an
independent performance validation. Similar validations were conducted with the
SED modelling and fitting tool MAGPHYS and modified black body functions to
test for model dependency. We demonstrate a clear improvement in agreement
between the flux densities extracted with XID+ and existing data at other
wavelengths when using the new informed Gaussian prior over the original
uninformed prior. The residuals between F and F were calculated. For
the Gaussian prior, these residuals, expressed as a multiple of the ALMA error
(), have a smaller standard deviation, 7.95 for the Gaussian
prior compared to 12.21 for the flat prior, reduced mean, 1.83
compared to 3.44, and have reduced skew to positive values, 7.97
compared to 11.50. These results were determined to not be significantly model
dependent. This results in statistically more reliable SPIRE flux densities.Comment: 8 pages, 7 figures, 3 tables. Accepted for publication in A&
A multideterminant assessment of mean field methods for the description of electron transfer in the weak coupling regime
Multideterminant calculations have been performed on model systems to
emphasize the role of many-body effects in the general description of charge
quantization experiments. We show numerically and derive analytically that a
closed-shell ansatz, the usual ingredient of mean-field methods, does not
properly describe the step-like electron transfer characteristic in weakly
coupled systems. With the multideterminant results as a benchmark, we have
evaluated the performance of common ab initio mean field techniques, such as
Hartree Fock (HF) and Density Functional Theory (DFT) with local and hybrid
exchange correlation functionals, with a special focus on spin-polarization
effects. For HF and hybrid DFT, a qualitatively correct open-shell solution
with distinct steps in the electron transfer behaviour can be obtained with a
spin-unrestricted (i.e., spin-polarized) ansatz though this solution differs
quantitatively from the multideterminant reference. We also discuss the
relationship between the electronic eigenvalue gap and the onset of charge
transfer for both HF and DFT and relate our findings to recently proposed
practical schemes for calculating the addition energies in the Coulomb blockade
regime for single molecule junctions from closed-shell DFT within the local
density approximation
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