The Impact of Foreign Aid on Government Spending, Revenue and Domestic Borrowing in Ethiopia

The main aim of this Working Paper is to assess the impact of foreign aid inflows on public expenditure, revenue and domestic borrowing in Ethiopia. The paper provides a literature overview of the fiscal effects of aid, and then applies a fiscal response model to Ethiopian data for the period 1964-2005. Since the empirical literature finds little evidence of common cross-country patterns, this highlights the important role that country-specific circumstances play in determining fiscal outcomes. By studying the particular fiscal dynamics in Ethiopia, the paper finds that foreign aid has had a positive impact on government investment, while its effect on current expenditure has been less pronounced. Moreover, by disaggregating aid inflows into grants and foreign lending, the paper is able to analyse their specific roles and impacts. The results support the conclusion that aid inflows increase public investment, with loans having a stronger impact than grants. Both aid grants and loans have a strong negative effect on domestic borrowing, suggesting that aid and domestic financing are close substitutes. Finally, the results also appear to support the hypothesis that higher aid flows displace domestic revenues. However, this particular finding does not seem to be robust across the sample.Foreign Aid, Aid Effectiveness, Fiscal Response Literature, Ethiopia

Cluster-cluster aggregation with particle replication and chemotaxy: a simple model for the growth of animal cells in culture

Aggregation of animal cells in culture comprises a series of motility, collision and adhesion processes of basic relevance for tissue engineering, bioseparations, oncology research and \textit{in vitro} drug testing. In the present paper, a cluster-cluster aggregation model with stochastic particle replication and chemotactically driven motility is investigated as a model for the growth of animal cells in culture. The focus is on the scaling laws governing the aggregation kinetics. Our simulations reveal that in the absence of chemotaxy the mean cluster size and the total number of clusters scale in time as stretched exponentials dependent on the particle replication rate. Also, the dynamical cluster size distribution functions are represented by a scaling relation in which the scaling function involves a stretched exponential of the time. The introduction of chemoattraction among the particles leads to distribution functions decaying as power laws with exponents that decrease in time. The fractal dimensions and size distributions of the simulated clusters are qualitatively discussed in terms of those determined experimentally for several normal and tumoral cell lines growing in culture. It is shown that particle replication and chemotaxy account for the simplest cluster size distributions of cellular aggregates observed in culture.Comment: 14 pages, 8 figures, to appear on Jsta

New Numerical Results Indicate a Half-Filling SU(4) Kondo State in Carbon Nanotubes

Numerical calculations simulate transport experiments in carbon nanotube quantum dots (P. Jarillo-Herrero et al., Nature 434, 484 (2005)), where a strongly enhanced Kondo temperature T_K ~ 8K was associated with the SU(4) symmetry of the Hamiltonian at quarter-filling for an orbitally double-degenerate single-occupied electronic shell. Our results clearly suggest that the Kondo conductance measured for an adjacent shell with T_K ~ 16K, interpreted as a singlet-triplet Kondo effect, can be associated instead to an SU(4) Kondo effect at half-filling. Besides presenting spin-charge Kondo screening similar to the quarter-filling SU(4), the half-filling SU(4) has been recently associated to very rich physical behavior, including a non-Fermi-liquid state (M. R. Galpin et al., Phys. Rev. Lett. 94, 186406 (2005)).Comment: 7 pages, 7 figure