3,330 research outputs found

    Filaments as Possible Signatures of Magnetic Field Structure in Planetary Nebulae

    Full text link
    We draw attention to the extreme filamentary structures seen in high-resolution optical images of certain planetary nebulae. We determine the physical properties of the filaments in the nebulae IC 418, NGC 3132, and NGC 6537, and based on their large length-to-width ratios, longitudinal coherence, and morphology, we suggest that they may be signatures of the underlying magnetic field. The fields needed for the coherence of the filaments are probably consistent with those measured in the precursor circumstellar envelopes. The filaments suggest that magnetic fields in planetary nebulae may have a localized and thread-like geometry.Comment: 26 pages with 7 figures. To be published in PASP. For full resolution images see http://physics.nyu.edu/~pjh

    A search for CO+ in planetary nebulae

    Get PDF
    We have carried out a systematic search for the molecular ion CO+ in a sample of 8 protoplanetary and planetary nebulae in order to determine the origin of the unexpectedly strong HCO+ emission previously detected in these sources. An understanding of the HCO+ chemistry may provide direct clues to the physical and chemical evolution of planetary nebulae. We find that the integrated intensity of the CO+ line may be correlated with that of HCO+, suggesting that the reaction of CO+ with molecular hydrogen may be an important formation route for HCO+ in these planetary nebulae.Comment: 6 pages, 4 figures, accepted for publication in MNRA

    The Middle East competitiveness report: regional and territorial analysis

    Get PDF
    This report explores the extent to which Middle Eastern regions have generated relatively high or low levels of competitiveness. Whilst many Middle Eastern regions may owe some of their competitiveness to the natural advantages of oil reserves, for others their competitiveness has been achieved through other means. Their small size and high degree of autonomy means that many of the regions are effectively independent states. Middle Eastern nations and their regions have been characterized by some as ‘rentier states’ (Brach, 2009), whereby a rent-seeking culture characterized by traits such as a large welfare deadweight loss, a perception of the market as rewarding the rich and well-connected, and a focus on rent capture rather than innovation (Krueger, 1974), is likely to hold back regional competitiveness. As Rodrik et al. (2004) find, institutions are often more important than geography and trade integration for economic development, and it is quite conceivable that the unique political economy of Middle Eastern regions will have profound effects on both their overall competitiveness and also the sources of this competitiveness

    Central subspaces review: methods and applications

    Get PDF
    Central subspaces have long been a key concept for sufficient dimension reduction. Initially constructed for solving problems in the p n . In this article we review the theory of central subspaces and give an updated overview of central subspace methods for the p ≤ n , p > n and big data settings. We also develop a new classification system for these techniques and list some R and MATLAB packages that can be used for estimating the central subspace. Finally, we develop a central subspace framework for bioinformatics applications and show, using two distinct data sets, how this framework can be applied in practice

    An automatic data system for vibration modal tuning and evaluation

    Get PDF
    A digitally based automatic modal tuning and analysis system developed to provide an operational capability beginning at 0.1 hertz is described. The elements of the system, which provides unique control features, maximum operator visibility, and rapid data reduction and documentation, are briefly described; and the operational flow is discussed to illustrate the full range of capabilities and the flexibility of application. The successful application of the system to a modal survey of the Skylab payload is described. Information about the Skylab test article, coincident-quadrature analysis of modal response data, orthogonality, and damping calculations is included in the appendixes. Recommendations for future application of the system are also made
    • …
    corecore