9,541 research outputs found

    Directed transport of active particles over asymmetric energy barriers

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    We theoretically and numerically investigate the transport of active colloids to target regions, delimited by asymmetric energy barriers. We show that it is possible to introduce a generalized effective temperature that is related to the local variance of particle velocities. The stationary probability distributions can be derived from a simple diffusion equation in the presence of an inhomogeneous effective temperature resulting from the action of external force fields. In particular, transitions rates over asymmetric energy barriers can be unbalanced by having different effective temperatures over the two slopes of the barrier. By varying the type of active noise, we find that equal values of diffusivity and persistence time may produce strongly varied effective temperatures and thus stationary distributions

    Grants and debt forgiveness in Africa : a descriptive analysis

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    The authors analyze the effects of bilateral debt forgiveness on 32 low-income countries in Africa (1984-93). Asking whether it makes a difference for recipient countries to receive pure grants rather that official development assistance (ODA) debt relief, they focus on how one form of aid or the other affects the countries'import capacity. They conclude that: a) grants allowed recipient countries to significantly expand their import capacity for 1984-93 as grants and import capacity have been increasing since 1984. But the increasing share of concessional lending and debt relief in recent years has not allowed these countries to reduce total indebtedness nor solve debt overhang. b) the biggest recipients of debt relief also received the lion's share of the pure grants increase. Debt forgiveness and pure grants were allocated not entirely consistent with standard economic hierarchies. c) bilateral ODA debt forgiveness appears to be neutral in the sense of not having any significant impact on import capacity. During 1989-93, multilateral lending replaced the bilateral lending decrease caused by an increase in grants. d) private creditors have typically withdrawn money as grants increased. And debt relief has had a crowding-out effect on new lending. Bilateral donors are switching their development finance to Africa from concessional and non-concessional lending to a combination of pure grants and ODA relief.Payment Systems&Infrastructure,Banks&Banking Reform,Public Sector Economics&Finance,Municipal Financial Management,Public&Municipal Finance,Urban Economics,Municipal Financial Management,Banks&Banking Reform,Public Sector Economics&Finance,Public&Municipal Finance

    Inflation in (Super-)renormalizable Gravity

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    We investigate a (super-)renormalizable and ghost-free theory of gravity, showing that under a natural (exponential) ansatz of the form factor and a suitable truncation it can give rise to the Starobinsky inflationary theory in cosmological frameworks, and thus offering a theoretical justification of its origin. We study the corresponding inflationary evolution and we examine the generation of curvature perturbations, adapting the f(R)f(R)-like equations in a symmetry-reduced FLRW metric. Furthermore, we analyze how the ultraviolet regime of a simply renormalizable and unitary theory of gravity is also compatible with the Starobinsky action, and hence we show that such a theory could account for an inflationary phase of the Universe in the ultraviolet regime.Comment: 7 page
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