Regions of star formation: chemical issues. Discussion session

This is an electronic version of the lecture presented at the Astronomical Society of the Pacific Conference held in Granada, Spain, 24-28 September, 2002

Smilansky's model of irreversible quantum graphs, II: the point spectrum

In the model suggested by Smilansky one studies an operator describing the interaction between a quantum graph and a system of K one-dimensional oscillators attached at different points of the graph. This paper is a continuation of our investigation of the case K>1. For the sake of simplicity we consider K=2, but our argument applies to the general situation. In this second paper we apply the variational approach to the study of the point spectrum.Comment: 18 page

The effects of turbulence intensity on the downstream performance of horizontal axis tidal stream turbines

This study focuses on a comparison of model results from a blade element momen- tum computational fluid dynamics (BEM-CFD) steady state RANS model, and a BEMT model that accounts for the wake generated from upstream turbines using analytic expressions. Rotor forces are calculated using 3D hydrofoil profile data. Both techniques are validated against ex- isting experimental data, and then used to assess the power extraction of downstream turbines. Turbulent inflow conditions of 3% and 7% are applied, and the results of power extraction as- sessed. Particular attention is paid to the velocity field, with respect to the downstream wake, to assess how the turbulence characteristics effect the recovery rate and downstream power potential. Both models highlight the different recovery rates of the two turbulent conditions

Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters

We present Gemini optical spectroscopy of 23 young star clusters in NGC3256. We find that the cluster ages range are from few Myr to ~150 Myr. All these clusters are relatively massive (2--40)x 10^{5} \msun$ and appear to be of roughly 1.5 \zo metallicity. The majority of the clusters in our sample follow the same rotation curve as the gas and hence were presumably formed in the molecular-gas disk. However, a western subsample of five clusters has velocities that deviate significantly from the gas rotation curve. These clusters may either belong to the second spiral galaxy of the merger or may have formed in tidal-tail gas falling back into the system. We discuss our observations in light of other known cluster populations in merging galaxies, and suggest that NGC 3256 is similar to Arp 220, and hence may become an Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation rate increases. Some of the clusters which appeared as isolated in our ground-based images are clearly resolved into multiple sub-components in the HST-ACS images. The same effect has been observed in the Antennae galaxies, showing that clusters are often not formed in isolation, but instead tend to form in larger groups or cluster complexes.Comment: 20 pages, 10 figures, 3 tables; Accepted Ap

A comparison of numerical modelling techniques for tidal stream turbine analysis

To fully understand the performance of tidal stream turbines for the creation of ocean ren wable energy, a range of computational models is required. We review and compare results from several models at different length scales. Models under review include blade element momentum theory (BEMT), blade element actuation disk RANS-CFD, blade- resolved RANS-CFD and coastal models based on the shallow water equations. Three sets of experimental results are used for model validation

Spatial Analyses of Oral Polio Vaccine Transmission in an Community Vaccinated With Inactivated Polio Vaccine.

Background: Understanding the spatial dynamics of oral polio vaccine (OPV) transmission will improve resource targeting. Mexico provides a natural laboratory, as it uses inactivated polio vaccine routinely as well as OPV bi-annually. Methods: Using geospatial maps, we measured the distance and density of OPV vaccinees' shedding in the areas nearest to unvaccinated households in 3 Mexican villages. Comparison of transmission to unvaccinated households utilized a mixed effects logistic regression with random effects for household and time, adjusted for age, gender, area, and running water. Results: The median distance from an unvaccinated household to its nearest OPV-shedding household was 85 meters (interquartile range, 46-145) and the median number of vaccinees shedding OPV within 200 m was 3 (2-6). Transmission to unvaccinated households occurred by day 1. There was no association (odds ratio [OR] 1.04; 95% credible interval [CrI] 0.92-1.16) between the distance from OPV shedding and the odds of transmission. The number of OPV vaccinees shedding within 200 m came close to a significant association with unvaccinated transmission (OR 0.93; CrI 0.84-1.01), but this was not the case for households 100 or 500 m apart. Results were consistent across the 3 villages. Conclusions: Geospatial analysis did not predict community transmission from vaccinated to unvaccinated households, because OPV use resulted in rapid, low transmission levels. This finding supports the global cessation of OPV

Spherical coupled-cluster theory for open-shell nuclei

A microscopic description of nuclei is important to understand the nuclear shell-model from fundamental principles. This is difficult to achieve for more than the lightest nuclei without an effective approximation scheme. The purpose of this paper is to define and evaluate an approximation scheme that can be used to study nuclei that are described as two particles attached to a closed (sub-)shell nucleus. The equation-of-motion coupled-cluster formalism has been used to obtain ground and excited state energies. This method is based on the diagonalization of a non-Hermitian matrix obtained from a similarity transformation of the many-body nuclear Hamiltonian. A chiral interaction at the next-to-next-to-next-to leading order using a cutoff at 500 MeV was used. The ground state energies of ${}^6$Li and ${}^6$He were in good agreement with a no-core shell-model calculation using the same interaction. Several excited states were also produced with overall good agreement. Only the $J^\pi=3^+$ excited state in ${}^6$Li showed a sizable deviation. The ground state energies of ${}^{18}$O, ${}^{18}$F and ${}^{18}$Ne were converged, but underbound compared to experiment. Moreover, the calculated spectra were converged and comparable to both experiment and shell-model studies in this region. Some excited states in ${}^{18}$O were high or missing in the spectrum. It was also shown that the wave function for both ground and excited states separates into an intrinsic part and a Gaussian for the center-of-mass coordinate. Spurious center-of-mass excitations are clearly identified.Comment: 23 pages, 17 figures. Accepted for publication in PR

Traditional turbulence methods and novel visualisation techniques for coastal flow model in order to deploy tidal stream turbines

Characteristics of flow in the coastal regions are strongly influenced by the topography of the seabed and understanding of these features is necessary before installation of tidal stream turbines (TST). In this paper, the bathymetry of a potential TST deployment site is surveyed using an echosounder and the resulting data is used in the development of the geometric model. The steady state k-ɛ and transient Large Eddy Simulation (LES) turbulence methods are employed. The stream surface visualisation method employed has important inherent characteristics that can enhance the visual perception of complex flow structures [1]. In this method lighting and shading reinforce the perception of shape and depth, images or textures can be mapped to the surface primitives providing additional visual information, colour and transparency can be used to convey additional data attributes. The results of all cases are compared with the flow data transect gathered by Acoustic Doppler Current Profiler (ADCP). It has been understood that the k-ɛ method can predict the flow pattern with relatively good accuracy near the main features of the domain and the LES model has the ability to simulate some important flow patterns because of the bathymetry