7,519 research outputs found
Conformal Covariance Subalgebras
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
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
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)
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
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
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