Efficient Searches for r-Process-Enhanced, Metal-Poor Stars

Neutron-capture-enhanced, metal-poor stars are of central importance to developing an understanding of the operation of the r-process in the early Galaxy, thought to be responsible for the formation of roughly half of all elements beyond the iron peak. A handful of neutron-capture-rich, metal-poor stars with [Fe/H] < -2.0 have already been identified, including the well known r-process-enhanced stars CS 22892-052 and CS 31082-001. However, many questions of fundamental interest can only be addressed with the assemblage of a much larger sample of such stars, so that general properties can be distinguished. We describe a new effort, HERES: The Hamburg/ESO R-Process-Enhanced Star survey, nearing completion, which will identify on the order of 5-10 additional highly r-process-enhanced, metal-poor stars, and in all likelihood, a similar or greater number of mildly r-process-enhanced, metal-poor stars in the halo of the Galaxy. HERES is based on rapid "snapshot" spectra of over 350 candidate halo giants with [Fe/H] < -2.0, obtained at moderately high resolution, and with moderate signal-to-noise ratios, using the UVES spectrograph on the European VLT 8m telescope.Comment: Contributed paper to The Eighth Nuclei in the Cosmos conference, to appear (in refereed form) in Nuclear Physics

Analytical approximations for the orientation distribution of small dipolar particles in steady shear flows

Analytic approximations are obtained to solutions of the steady Fokker-Planck equation describing the probability density functions for the orientation of dipolar particles in a steady, low-Reynolds-number shear flow and a uniform external field. Exact computer algebra is used to solve the equation in terms of a truncated spherical harmonic expansion. It is demonstrated that very low orders of approximation are required for spheres but that spheroids introduce resolution problems in certain flow regimes. Moments of the orientation probability density function are derived and applications to swimming cells in bioconvection are discussed. A separate asymptotic expansion is performed for the case in which spherical particles are in a flow with high vorticity, and the results are compared with the truncated spherical harmonic expansion. Agreement between the two methods is excellent

Long lasting instabilities in granular mixtures

We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurence of instabilities which can last several hours. We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurence of giant fluctuations in the fraction of grain species along the surface during the unstable periods.Comment: 10 pages, 10 figures, (2002

Temperature-dependent molecular absorption cross sections for exoplanets and other atmospheres

Exoplanets, and in particular hot ones such as hot Jupiters, require a very significant quantities of molecular spectroscopic data to model radiative transport in their atmospheres or to interpret their spectra. This data is commonly provided in the form of very extensive transition line lists. The size of these line lists is such that constructing a single model may require the consideration of several billion lines. We present a procedure to simplify this process based on the use of cross sections. Line lists for water, H$_3^+$, HCN /HNC and ammonia have been turned into cross sections on a fine enough grid to preserve their spectroscopic features. Cross sections are provided at a fixed range of temperatures and an interpolation procedure which can be used to generate cross sections at arbitrary temperatures is described. A web-based interface (www.exomol.com/xsec) has been developed to allow astronomers to download cross sections at specified temperatures and spectral resolution. Specific examples are presented for the key water molecule.Comment: Icarus (submitted

The Effect of Flow Regulation on Channel Geomorphic Unit (CGU) Composition in the Soča River, Slovenia.

This paper sets out to examine the effects of flow regulation on the size, spatial distribution and connectivity of physical habitats or channel geomorphic units (CGU) of an upland river system in Slovenia. A river channel survey was completed along three reaches (totalling 14.3km) of the Soča River in order compare an unregulated stretch (reach 1), with two regulated reaches with lower discharges, i.e. a bypassed section that experiences significant flow reduction (reach 2), and a stretch regulated by dam operation (reach 3). CGU’s were classified according to a modified version of the Hawkins et al (1993) system, and mapped on foot and from a boat using a combination of visual assessment and physical measurement. Mapping-grade GPS was used to locate CGU boundaries to sub-metre accuracy, and the application of GIS (MapInfo) enabled the description and analysis of the longitudinal distribution of CGU’s along each reach. Results demonstrated significant differences in the CGU composition between the unregulated and regulated reaches. The unregulated stretch (reach 1) was dominated by the glides (55%) with relatively fast-flowing and turbulent features (runs, riffles and rapids) making up the rest of the reach. The dominant feature of both of the regulated reaches were the slow flowing pool CGU’s occupying 44% of the bypassed section (reach 2), and 76% of the dam regulated section (reach 3), with glides, runs, riffles and rapids forming the remainder of the CGU’s. Physical measurements highlighted the extent to which the reduced discharge in the regulated reaches was dewatering the channel and reducing the size of the CGU’s. The average CGU size in the unregulated stretch (reach 1) was 58m2 of water area per m of channel length (m2/m) compared to 18.42m2/m in the reach 2, and 29.22m2/m in reach 3. CGU’s tended to be shorter, and hence there was greater habitat division or fragmenta-tion evident in the two regulated reaches, particularly the bypassed section. For example, there were on aver-age 6.81 CGU’s per km in the unregulated reach (reach 1), 18.12 CGU/km in reach 2, and 8.08 CGU/km in reach 3. This study suggests that in the Soča River under the flow conditions present during the survey, flow regula-tion alters the dominant types of CGU’s present (to slower flowing and less turbulent features), significantly reduces the size of CGU’s, and affects the longitudinal distribution of types by reducing habitat connectivity and creating greater habitat fragmentation

A comparison of Voxel compression mapping & longitudinal Voxel-Based morphometry

Clinical motivation: Serial brain imaging can reveal patterns of change over time with important clinical implications for neurodegenerative disease [1]. We investigate the performance of four analysis methods, in terms of a comparison of 20 patients with probable AD to 20 age- and sex-matched controls, characterising differences in change from baseline to later scans