Spin Observables for Polarizing Antiprotons

The PAX project at GSI Darmstadt plans to polarize an antiproton beam by repeated interaction with a hydrogen target in a storage ring. Many of the beam particles are required to remain within the ring after interaction with the target, so small scattering angles are important. Hence we concentrate on low momentum transfer (small t), a region where electromagnetic effects dominate the hadronic effects. A colliding beam of polarized electrons with energy sufficient to provide scattering of antiprotons beyond ring acceptance may polarize an antiproton beam by spin filtering. Expressions for spin observables are provided and are used to estimate the rate of buildup of polarization of an antiproton beam.Comment: 4 pages, 2 figures, to be published in the Proceedings of the 17th International Spin Physics Symposium (SPIN 2006), Kyoto, Japan; October 2-7, 200

Structures Produced by the Collision of Extragalactic Jets with Dense Clouds

We have investigated how several parameters can affect the results of a collision between an extragalactic jet and a dense, intergalactic cloud, through a series of hydrodynamic simulations. Such collisions are often suggested to explain the distorted structures of some radio jets. However, theoretical studies of this mechanism are in conflict over whether it can actually reproduce the observations. The parameters are the Mach number, and the relative densities of the jet and the cloud to the ambient medium. Using a simple prescription we have produced synthetic radio images for comparison with observations. These show that a variety of structures may be produced from simple jet-cloud collisions. We illustrate this with a few examples, and examine the details in one case. In most cases we do not see a clear, sustained deflection. Lighter jets are completely disrupted. The most powerful jets produce a hotspot at the impact which outshines any jet emission and erode the cloud too quickly to develop a deflected arm. It appears that moderate Mach numbers and density contrasts are needed to produce bends in the radio structure. This explains the apparent conflict between theoretical studies, as conclusions were based on different values of these parameters. Shocks are produced in the ambient medium that might plausibly reproduce the observed alignment of the extended emission line regions with the radio axis.Comment: 21 pages, 11 figures. Submitted to MNRAS. Also available in html version at http://www.doc.mmu.ac.uk/STAFF/S.Higgins/jcmnpaper/jc_mn.htm

Superconductivity in Heavy Alkaline-Earths Intercalated Graphites

We report the discovery of superconductivity below 1.65(6) K in Sr-intercalated graphite SrC6, by susceptibility and specific heat (Cp) measurements. In comparison with CaC6, we found that the anisotropy of the upper critical fields for SrC6 is much reduced. The Cp anomaly at Tc is smaller than the BCS prediction indicating an anisotropic superconducting gap for SrC6 similar to CaC6. The significantly lower Tc of SrC6 as compared to CaC6 can be understood in terms of "negative" pressure effects, which decreases the electron-phonon coupling for both in-plane intercalant and the out-of-plane C phonon modes. We observed no superconductivity for BaC6 down to 0.3 K.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

The precision of international market sampling for North Sea herring and its influence on assessment

Market sampling is a key source of data for catch-at-age-based assessment. Little has been documented about the influence of potential error in these data on the precision of assessments and the management information they produce. This paper presents the results of a study of the precision of North Sea herring fish market sampling carried out by the UK, Denmark and the Netherlands. Data from eight years of market sampling were analysed to obtain the precision of estimated numbers-at-age in the catch. The market sample data was then used to estimate 1000 realisations of the international catch-at-age and mean weightsat- age in the catch. Three methods of estimating the variability of missing catch data were used and three options for the catch-at-age matrices were computed. These base datasets were utilised to obtain 1000 assessments conditional on the ICA (Integrated Catch-at-age Analysis) model. From the outcome of these assessments the influence of the market sampling programmes on the management of the stock are presented as 95␌onfidence intervals on the main management parameters (recruitment, SSB, F0-1 and F2-6). In addition, the influence of missing data is estimated. The implications of our conclusions on the requirements from a market sampling programme are discusse