QSO Absorption Line Constraints on Intragroup High-Velocity Clouds

We show that the number statistics of moderate redshift MgII and Lyman limit absorbers may rule out the hypothesis that high velocity clouds are infalling intragroup material.Comment: 4 pages, no figures; submitted to Astrophysical Journal Letters; revised version, more general and includes more about Braun and Burton CHVC

Performance of three-photon PET imaging: Monte Carlo simulations

We have recently introduced the idea of making use of three-photon positron annihilations in positron emission tomography. In this paper the basic characteristics of the three-gamma imaging in PET are studied by means of Monte Carlo simulations and analytical computations. Two typical configurations of human and small animal scanners are considered. Three-photon imaging requires high energy resolution detectors. Parameters currently attainable by CdZnTe semiconductor detectors, the technology of choice for the future development of radiation imaging, are assumed. Spatial resolution is calculated as a function of detector energy resolution and size, position in the field of view, scanner size, and the energies of the three gamma annihilation photons. Possible ways to improve the spatial resolution obtained for nominal parameters: 1.5 cm and 3.2 mm FWHM for human and small animal scanners, respectively, are indicated. Counting rates of true and random three-photon events for typical human and small animal scanning configurations are assessed. A simple formula for minimum size of lesions detectable in the three-gamma based images is derived. Depending on the contrast and total number of registered counts, lesions of a few mm size for human and sub mm for small animal scanners can be detected

The Advantage of Increased Resolution in the Study of Quasar Absorption Systems

We compare a new R = 120,000 spectrum of PG1634+706 (z_QSO = 1.337,m_V = 14.9) obtained with the HDS instrument on Subaru to a R = 45, 000 spectrum obtained previously with HIRES/Keck. In the strong MgII system at z = 0.9902 and the multiple cloud, weak MgII system at z = 1.0414, we find that at the higher resolution, additional components are resolved in a blended profile. We find that two single-cloud weak MgII absorbers were already resolved at R = 45,000, to have b = 2 - 4 km/s. The narrowest line that we measure in the R = 120, 000 spectrum is a component of the Galactic NaI absorption, with b = 0.90+/-0.20 km/s. We discuss expectations of similarly narrow lines in various applications, including studies of DLAs, the MgI phases of strong MgII absorbers, and high velocity clouds. By applying Voigt profile fitting to synthetic lines, we compare the consistency with which line profile parameters can be accurately recovered at R = 45,000 and R = 120,000. We estimate the improvement gained from superhigh resolution in resolving narrowly separated velocity components in absorption profiles. We also explore the influence of isotope line shifts and hyperfine splitting in measurements of line profile parameters, and the spectral resolution needed to identify these effects. Super high resolution spectra of quasars, which will be routinely possible with 20-meter class telescopes, will lead to greater sensitivity for absorption line surveys, and to determination of more accurate physical conditions for cold phases of gas in various environments.Comment: To appear in AJ. Paper with better resolution images available at http://www.astro.psu.edu/users/anand/superhigh.AJ.pd

Identification of diverse database subsets using property-based and fragment-based molecular descriptions

This paper reports a comparison of calculated molecular properties and of 2D fragment bit-strings when used for the selection of structurally diverse subsets of a file of 44295 compounds. MaxMin dissimilarity-based selection and k-means cluster-based selection are used to select subsets containing between 1% and 20% of the file. Investigation of the numbers of bioactive molecules in the selected subsets suggest: that the MaxMin subsets are noticeably superior to the k-means subsets; that the property-based descriptors are marginally superior to the fragment-based descriptors; and that both approaches are noticeably superior to random selection

Modelling commuting catchments in Ireland: a hierarchical approach using GIS.

Over recent years there has emerged an increased awareness of the importance of strategic spatial planning and of the extent to which concepts such as place and space really matter (Faludi, 2000). An enhanced understanding of the geography of living and the economy requires not only a knowledge of where people and objects are but also of how those places relate to one another to create functional spaces. This requires fundamentally sound data on movement patterns, of which the most important is probably the daily journey to work (Horner, 1999, McCabe, 2006 Pers Comm). In this paper we examine spatial modelling approaches to commuting patterns using data from the CSO 2002 Census of Population (CSO 2003a, CSO 2003b. CSO 2004a). This is a particularly apposite time to undertake this research. A number of national strategic initiatives including the next Irish National Development Plan and the current National Spatial Strategy provide a clear policy context for the study (Morgenroth and Fitzgerald,2006). Additionally it is the specific intent of the CSO in providing this data set to stimulate geo-computational analysis and modelling. This research aims to map travel to work flows in 2002 from the 15% national anonymised individual sample (known as the POWSAR data set) and secondly to investigate the technical production of new Travel Catchments Areas (TCAs) for the state as a whole