1,461 research outputs found
Trade Liberalisation, Efficiency and South Africa's Sugar Industry
This paper reports the results of a computable general equilibrium (CGE) analysis of the South African sugar industry. The study was inspired by analyses of the EU South Africa Free Trade Agreement that indicated the importance of sugar exports to the welfare gains from agricultural trade liberalisation and by the increasing pressure upon OECD countries to reform their sugar (trade) policies. In addition to the effects of trade liberalisation this study also considers the implications of increases in the efficiency with which sugarcane is converted to raw sugar, which is an important determinant of the competitiveness of sugar production and exports. The results indicate that there would be substantial welfare gains across all household groups and that overall agricultural producers in South Africa should benefit; however there are substantial variations in the impact upon agricultural producers in different provinces, with farmers in some provinces facing reductions in the profitability of farming
Quasinormal Modes Beyond Kerr
The quasinormal modes (QNMs) of a black hole spacetime are the free, decaying
oscillations of the spacetime, and are well understood in the case of Kerr
black holes. We discuss a method for computing the QNMs of spacetimes which are
slightly deformed from Kerr. We mention two example applications: the
parametric, turbulent instability of scalar fields on a background which
includes a gravitational QNM, and the shifts to the QNM frequencies of Kerr
when the black hole is weakly charged. This method may be of use in studies of
black holes which are deformed by external fields or are solutions to
alternative theories of gravity.Comment: Proceedings of the Sant Cugat Forum on Astrophysics (2014). Session
on 'Gravitational Wave Astrophysics.' 7 page
Continuous phase transition in polydisperse hard-sphere mixture
In a previous paper (J. Zhang {\it et al.}, J. Chem. Phys. {\bf 110}, 5318
(1999)) we introduced a model for polydisperse hard sphere mixtures that is
able to adjust its particle-size distribution. Here we give the explanation of
the questions that arose in the previous description and present a consistent
theory of the phase transition in this system, based on the Percus-Yevick
equation of state. The transition is continuous, and like Bose-Einstein
condensation a macroscopic aggregate is formed due to the microscopic
interactions. A BMCSL-like treatment leads to the same conclusion with slightly
more accurate predictions.Comment: 7 pages including 5 figures in revte
Quasinormal modes and stability of the rotating acoustic black hole: numerical analysis
The study of the quasinormal modes (QNMs) of the 2+1 dimensional rotating
draining bathtub acoustic black hole, the closest analogue found so far to the
Kerr black hole, is performed. Both the real and imaginary parts of the
quasinormal (QN) frequencies as a function of the rotation parameter B are
found through a full non-linear numerical analysis. Since there is no change in
sign in the imaginary part of the frequency as B is increased we conclude that
the 2+1 dimensional rotating draining bathtub acoustic black hole is stable
against small perturbations.Comment: 6 pages, ReVTeX4. v2. References adde
Asymptotic Quasinormal Frequencies of Different Spin Fields in Spherically Symmetric Black Holes
We consider the asymptotic quasinormal frequencies of various spin fields in
Schwarzschild and Reissner-Nordstr\"om black holes. In the Schwarzschild case,
the real part of the asymptotic frequency is ln3 for the spin 0 and the spin 2
fields, while for the spin 1/2, the spin 1, and the spin 3/2 fields it is zero.
For the non-extreme charged black holes, the spin 3/2 Rarita-Schwinger field
has the same asymptotic frequency as that of the integral spin fields. However,
the asymptotic frequency of the Dirac field is different, and its real part is
zero. For the extremal case, which is relevant to the supersymmetric
consideration, all the spin fields have the same asymptotic frequency, the real
part of which is zero. For the imaginary parts of the asymptotic frequencies,
it is interesting to see that it has a universal spacing of for all the
spin fields in the single-horizon cases of the Schwarzschild and the extreme
Reissner-Nordstr\"om black holes. The implications of these results to the
universality of the asymptotic quasinormal frequencies are discussed.Comment: Revtex, 17 pages, 3 eps figures; one table, some remarks and
references added to section I
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
Dirac Quasinormal modes of Schwarzschild black hole
The quasinormal modes (QNMs) associated with the decay of Dirac field
perturbation around a Schwarzschild black hole is investigated by using
continued fraction and Hill-determinant approaches. It is shown that the
fundamental quasinormal frequencies become evenly spaced for large angular
quantum number and the spacing is given by . The angular quantum number has the
surprising effect of increasing real part of the quasinormal frequencies, but
it almost does not affect imaginary part, especially for low overtones. In
addition, the quasinormal frequencies also become evenly spaced for large
overtone number and the spacing for imaginary part is
which is same as that of the
scalar, electromagnetic, and gravitational perturbations.Comment: 14 pages, 5 figure
The size, concentration, and growth of biodiversity-conservation nonprofits
Nonprofit organizations play a critical role in efforts to conserve biodiversity. Their success in this regard will be determined in part by how effectively individual nonprofits and the sector as a whole are structured. One of the most fundamental questions about an organizationâs structure is how large it should be, with the logical counterpart being how concentrated the whole sector should be. We review empirical patterns in the size, concentration, and growth of over 1700 biodiversity-conservation nonprofits registered for tax purposes in the United States within the context of relevant economic theory. Conservation-nonprofit sizes vary by six to seven orders of magnitude and are positively skewed. Larger nonprofits access more revenue streams and hold more of their assets in land and buildings than smaller or midsized nonprofits do. The size of conservation nonprofits varies with the ecological focus of the organization, but the growth rates of nonprofits do not
Enhancement of the immunoregulatory potency of mesenchymal stromal cells by treatment with immunosuppressive drugs
Background aims Multipotent mesenchymal stromal cells (MSCs) are distinguished by their ability to differentiate into a number of stromal derivatives of interest for regenerative medicine, but they also have immunoregulatory properties that are being tested in a number of clinical settings. Methods We show that brief incubations with rapamycin, everolimus, FK506 or cyclosporine A increase the immunosuppressive potency of MSCs and other cell types. Results The treated MSCs are up to 5-fold more potent at inhibiting the induced proliferation of T lymphocytes in vitro. We show that this effect probably is due to adsorption of the drug by the MSCs during pre-treatment, with subsequent diffusion into co-cultures at concentrations sufficient to inhibit T-cell proliferation. MSCs contain measurable amounts of rapamycin after a 15-min exposure, and the potentiating effect is blocked by a neutralizing antibody to the drug. With the use of a pre-clinical model of acute graft-versus-host disease, we demonstrate that a low dose of rapamycin-treated but not untreated umbilical cordâderived MSCs significantly inhibit the onset of disease. Conclusions The use of treated MSCs may achieve clinical end points not reached with untreated MSCs and allow for infusion of fewer cells to reduce costs and minimize potential side effects
Auditing with accountability : shrinking the opportunity spaces for audit failure
In recent years a number of high-profile company failures have raised fundamental questions about the willingness and/or ability of auditors to exercise the professional scepticism necessary for the production of robust audits.
This report, co-written by Adam Leaver at the University of Sheffield and Leonard Seabrooke, Saila Stausholm and Duncan Wigan at Copenhagen Business School, examines the causes of those failures and makes a series of recommendations on how to resolve them.
The report argues that audit failure takes place within a particular configuration of economic, cultural and regulatory arrangements which create the 'opportunity spaces' for poor practice. Shrinking those opportunity spaces therefore requires a multi-dimensional response, including the structural separation of audit and non-audit functions, a more robust system of fines and the integration of a civil society voice into the reform process to prevent regulatory capture
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