7,443 research outputs found

    Conformal Covariance Subalgebras

    Full text link
    We give a direct Lie algebraic characterisation of conformal inclusions of chiral current algebras associated with compact, reductive Lie algebras. We use straightforward quantum field theoretic arguments and prove a long standing conjecture of Schellekens and Warner on grounds of unitarity and positivity of energy. We explore the structures found to characterise ``conformal covariance subalgebras'' and ``coset current algebras''.Comment: 9 pages, no figures; typos and minor improvement

    The profession of (agricultural) economists and the experience of transition

    Get PDF
    The objective of the paper is to survey the state of knowledge of economists and agricultural economists at the onset of transition and seventeen years later. The "standard" economic reasoning in the early nineties were based on neoclassical economics and documented was has been termed the Washington Consensus. It is shown that the discrepancy between expectations and reality as well as the evolution of institutional economics has challenged economists. A "blue print" favoured in the early nineties seems to be opposed by many economist nowadays. Agricultural economists have been influenced by the lines of thought in the main profession, but there approach became country-specific in early years of the transition period. Nevertheless, there are some open questions concerning assessment and approach in giving policy advice.Washington Consensus, land reform, farm organization, Teaching/Communication/Extension/Profession,

    Super-large Farms: The Importance of Institutions

    Get PDF
    There are many reasons for the evolution of super-farms in some of the CIS. This paper does not intend to elaborate on the whole set of reasons. There are already many studies which provide surveys on the background and the rationale of these organisations. This paper aims at focusing on one specific determinant of the rise of super-large farms, namely institutions. The focus is chosen as this determinant seems to have been overlooked, partly because it is completely beyond the neoclassical approach. Institutions as rules of the game can be classified into four levels according to Williamson. The paper mainly deals with embedded institutions. It is shown that these institutions are country-specific and vary widely across countries. It is argued that the evolution of super-large farms could only arise because cooperative and corporate farms survived up to bankruptcy and because embedded institutions impeded the foundation of family farms. Mental models of policy makers did contribute to the amalgation of corporate and cooperatives into super-large farms. However, it is noted that embedded institutions had such strong effects because markets did not work adequately and legislation and its enforcement was not supportive for the foundation of family farms. The paper ends with an evaluation from the economic point of view of the existence of super-large farms and with a projection of what may happen in the future.Agribusiness,

    An empirical initial-final mass relation from hot, massive white dwarfs in NGC 2168 (M35)

    Full text link
    The relation between the zero-age main sequence mass of a star and its white-dwarf remnant (the initial-final mass relation) is a powerful tool for exploration of mass loss processes during stellar evolution. We present an empirical derivation of the initial-final mass relation based on spectroscopic analysis of seven massive white dwarfs in NGC 2168 (M35). Using an internally consistent data set, we show that the resultant white dwarf mass increases monotonically with progenitor mass for masses greater than 4 solar masses, one of the first open clusters to show this trend. We also find two massive white dwarfs foreground to the cluster that are otherwise consistent with cluster membership. These white dwarfs can be explained as former cluster members moving steadily away from the cluster at speeds of <~0.5 km/s since their formation and may provide the first direct evidence of the loss of white dwarfs from open clusters. Based on these data alone, we constrain the upper mass limit of WD progenitors to be >=5.8 solar masses at the 90% confidence level for a cluster age of 150 Myr.Comment: 14 pages, 3 figures. Accepted for publication in the Astrophysical Journal Letters. Contains some acknowledgements not in accepted version (for space reasons), otherwise identical to accepted versio

    The White Dwarf Population in NGC 1039 (M34) and the White Dwarf Initial-Final Mass Relation

    Get PDF
    We present the first detailed photometric and spectroscopic study of the white dwarfs (WDs) in the field of the ~225 Myr old (log tau_cl = 8.35) open cluster NGC 1039 (M34) as part of the ongoing Lick-Arizona White Dwarf Survey. Using wide-field UBV imaging, we photometrically select 44 WD candidates in this field. We spectroscopically identify 19 of these objects as WDs; 17 are hydrogen-atmosphere DA WDs, one is a helium-atmosphere DB WD, and one is a cool DC WD that exhibits no detectable absorption lines. We find an effective temperature (T_eff) and surface gravity (log g) for each DA WD by fitting Balmer-line profiles from model atmospheres to the observed spectra. WD evolutionary models are then invoked to derive masses and cooling times for each DA WD. Of the 17 DAs, five are at the approximate distance modulus of the cluster. Another WD with a distance modulus 0.45 mag brighter than that of the cluster could be a double-degenerate binary cluster member, but is more likely to be a field WD. We place the five single cluster member WDs in the empirical initial-final mass relation and find that three of them lie very close to the previously derived linear relation; two have WD masses significantly below the relation. These outliers may have experienced some sort of enhanced mass loss or binary evolution; however, it is quite possible that these WDs are simply interlopers from the field WD population. Eight of the 17 DA WDs show significant CaII K absorption; comparison of the absorption strength with the WD distances suggests that the absorption is interstellar, though this cannot be confirmed with the current data.Comment: 24 pages, 13 figures. Accepted for publication in the Astronomical Journal. Figures 1, 2 and 3 reduced in resolutio
    • …