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

The mass of the black hole in GRS 1915+105: new constraints from IR spectroscopy

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large. Here we present spectroscopic analysis of medium-resolution IR VLT archival data of GRS 1915+105 in the K-band. We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radial velocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandhead emission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrain the black hole mass. We report on a possible way to measure the radial velocity utilising apparent H-band atomic absorption features and also discuss the general uncertainty of the system parameters of this well-studied objectComment: 7 pages, 7 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Gravitationally Lensed Gamma-Ray Bursts as Probes of Dark Compact Objects

If dark matter in the form of compact objects comprises a large fraction of the mass of the universe, then gravitational lensing effects on gamma-ray bursts are expected. We utilize BATSE and Ulysses data to search for lenses of different mass ranges, which cause lensing in the milli, pico, and femto regimes. Null results are used to set weak limits on the cosmological abundance of compact objects in mass ranges from 10$^{-16}$ to 10$^{-9}$ $M_{\odot}$. A stronger limit is found for a much discussed $\Omega = 0.15$ universe dominated by black holes of masses $\sim 10^{6.5} M_{\odot}$, which is ruled out at the $\sim$ 90% confidence level.Comment: 14 pages, 4 figures, fixed minor corrections. Accepted for publication in ApJ(L

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

Measurement Of Positron Annihilation Line Shapes With A Ge(Li) Detector

We observed that the annihilation radiation photopeak in a Ge(Li) detector is considerably broader than that of a γ ray of the same energy. It seems reasonable to assume that the increased width is the result of the Doppler broadening of the annihilation photopeak, i.e., the longitudinal Doppler shift of the radiations is measured, while the transverse shift is measured in the usual angular-correlation experiments. By using a computer stripping program to remove the distortion produced by the finite energy resolution of our detector, we obtain momentum distributions in agreement with those which have been published. Only one detector is necessary for these measurements, and all momentum channels are detected at once. However, the detector energy resolution severely limits the momentum resolution. Arguments are presented which indicate that no very large improvement in Ge(Li) detector resolution can be expected. © 1968 The American Physical Society