Targeting aid to the needy and deserving : nothing but promises?.

By reallocating aid to where it is needed most and where a productive use is most likely, donors could help alleviate poverty in developing countries. The rhetoric of donors suggests that this insight has increasingly shaped the allocation of aid. We assess the poverty and policy orientation of bilateral and multilateral aid in different ways. In addition to presenting stylized facts based on bivariate correlations, we apply a Tobit model that captures both altruistic and selfish donor motives. We find little evidence supporting the view that the targeting of aid has improved significantly. Most donors provide higher aid to relatively poor countries, but so far the fight against poverty has not resulted in a stronger focus on the most needy recipients. The estimation results reveal that the policy orientation of aid critically depends on how local conditions are measured. Applying the widely used Kaufmann index on the quality of institutions, almost all donors failed to direct aid predominantly to where local conditions were conducive to a productive use of inflows. The response of donors to changing institutional and policy conditions in recipient countries turns out to be fairly weak. In particular, we reject the proposition that multilateral aid is more targeted than bilateral aid in terms of rewarding poor countries with better policies and institutions.Entwicklungshilfe; Entwicklungskooperation; Armutspolitik; Wirtschaftspolitische Wirkungsanalyse; Entwicklungsländer;bilateral aid , multilateral aid , fight against poverty , economic policy assessment , quality of institutions;

Adjustment policies and economic growth in developing countries : is devaluation contractionary?.

Anpassungsprogramm des IWF; Wirtschaftspolitik; Entwicklung; Wechselkurspolitik; Entwicklungsländer;

Performance analysis of parallel gravitational NN-body codes on large GPU cluster

We compare the performance of two very different parallel gravitational $N$-body codes for astrophysical simulations on large GPU clusters, both pioneer in their own fields as well as in certain mutual scales - NBODY6++ and Bonsai. We carry out the benchmark of the two codes by analyzing their performance, accuracy and efficiency through the modeling of structure decomposition and timing measurements. We find that both codes are heavily optimized to leverage the computational potential of GPUs as their performance has approached half of the maximum single precision performance of the underlying GPU cards. With such performance we predict that a speed-up of $200-300$ can be achieved when up to 1k processors and GPUs are employed simultaneously. We discuss the quantitative information about comparisons of two codes, finding that in the same cases Bonsai adopts larger time steps as well as relative energy errors than NBODY6++, typically ranging from $10-50$ times larger, depending on the chosen parameters of the codes. While the two codes are built for different astrophysical applications, in specified conditions they may overlap in performance at certain physical scale, and thus allowing the user to choose from either one with finetuned parameters accordingly.Comment: 15 pages, 7 figures, 3 tables, accepted for publication in Research in Astronomy and Astrophysics (RAA

SMBH in Galactic Nuclei with Tidal Disruption of Stars

Tidal Disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct $N$-body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile and for the first time the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around the super massive black hole, we use the particle number and the tidal radius of black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, the tidal disruption rate scales with the particle number $N$ in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank & Rees (1976), which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is founded inside the cluster. Finally we make an estimation for the real galactic center based on our simulation results and the scaling analysis.Comment: 15 pages, 16 figures, accepted by Ap

Supermassive Black Holes in Galactic Nuclei with Tidal Disruption of Stars: Paper II - Axisymmetric Nuclei

Tidal Disruption of stars by supermassive central black holes from dense rotating star clusters is modelled by high-accuracy direct N-body simulation. As in a previous paper on spherical star clusters we study the time evolution of the stellar tidal disruption rate and the origin of tidally disrupted stars, now according to several classes of orbits which only occur in axisymmetric systems (short axis tube and saucer). Compared with that in spherical systems, we found a higher TD rate in axisymmetric systems. The enhancement can be explained by an enlarged loss-cone in phase space which is raised from the fact that total angular momentum $\bf J$ is not conserved. As in the case of spherical systems, the distribution of the last apocenter distance of tidally accreted stars peaks at the classical critical radius. However, the angular distribution of the origin of the accreted stars reveals interesting features. Inside the influence radius of the supermassive black hole the angular distribution of disrupted stars has a conspicuous bimodal structure with a local minimum near the equatorial plane. Outside the influence radius this dependence is weak. We show that the bimodal structure of orbital parameters can be explained by the presence of two families of regular orbits, namely short axis tube and saucer orbits. Also the consequences of our results for the loss cone in axisymmetric galactic nuclei are presented.Comment: 14 pages, 16 figures, accepted by Ap