A model for multifragmentation in heavy-ion reactions

From an experimental point of view, clear signatures of multifragmentation have been detected by different experiments. On the other hand, from a theoretical point of view, many different models, built on the basis of totally different and often even contrasting assumptions, have been provided to explain them. In this contribution we show the capabilities and the shortcomings of one of this models, a QMD code developed by us and coupled to the nuclear de-excitation module taken from the multipurpose transport and interaction code FLUKA, in reproducing the multifragmentation observations recently reported by the INDRA collaboration for the reaction Nb + Mg at a 30 MeV/A projectile bombarding energy. As far as fragment production is concerned, we also briefly discuss the isoscaling technique by considering reactions characterized by a different isospin asymmetry, and we explain how the QMD + FLUKA model can be applied to obtain information on the slope of isotopic yield ratios, which is crucially related to the symmetry energy of asymmetric nuclear matter.Comment: 8 pages, 2 figures, Proc. 12th International Conference on Nuclear Reaction Mechanisms, Varenna, Italy, June 15 - 19 200

Economic growth and investment in the Arab world

This paper analyses the economic growth performance in the Arab world over the last forty years. The Arab world has managed to reduce poverty performance despite its relatively disappointing growth performance. We relate this poor performance of both oil and non-oil producers to investment. Contrary to widespread belief, we do not find evidence that low quantity of investment is the main of low growth. The decline in the investment rate followed rather than preceded the reduction in the aggregate growth rate. We conclude that the low quality of investment projects is the key determinant of growth. The excessive reliance on public investment, the low quality of financial institutions, the bad business environment (due to political and social instability and to excessive public intervention and overregulation) and the low quality of human capital are important determinants of systematically unproductive investment decisions and, thus, low economic growth.Economic growth, investment, the Arab World

The Economic Tragedy of the XXth Century: Growth in Africa

The dismal growth performance of Africa is the worst economic tragedy of the XXth century. We document the evolution of per capita GDP for the continent as a whole and for subset of countries south of the Sahara desert. We document the worsening of various income inequality indexes and we estimate poverty rates and headcounts. We then analyze some of the central robust determinants of economic growth reported by Sala-i-Martin, Doppelhofer and Miller (2003) and project the annual growth rates Africa would have enjoyed if these key determinants had taken OECD rather than African values. Expensive investment goods, low levels of education, poor health, adverse geography, closed economies, too much public expenditure and too many military conflicts are seen as key explanations of the economic tragedy.

The economic tragedy of the XXth Century: Growth in Africa

The dismal growth performance of Africa is the worst economic tragedy of the XXth century. We document the evolution of per capita GDP for the continent as a whole and for subset of countries south of the Sahara desert. We document the worsening of various income inequality indexes and we estimate poverty rates and headcounts. We then analyze some of the central robust determinants of economic growth reported by Sala-i-Martin, Doppelhofer and Miller (2003) and project the annual growth rates Africa would have enjoyed if these key determinants had taken OECD rather than African values. Expensive investment goods, low levels of education, poor health, adverse geography, closed economies, too much public expenditure and too many military conflicts are seen as key explanations of the economic tragedy.Africa, determinants of growth, economic developement

Geostatistical interpretation of paleoceanographic data over large ocean basins - Reality and fiction

A promising approach to reconstruct oceanographic scenarios of past time slices is to drive numerical ocean circulation models with sea surface temperatures, salinities, and ice distributions derived from sediment core data. Set up properly, this combination of boundary conditions provided by the data and physical constraints represented by the model can yield physically consistent sets of three-dimensional water mass distribution and circulation patterns. This idea is not only promising but dangerous, too. Numerical models cannot be fed directly with data from single core locations distributed unevenly and, as it is the common case, scarcely in space. Conversely, most models require forcing data sets on a regular grid with no missing points, and some method of interpolation between punctual source data and model grid has to be employed. An ideal gridding scheme must retain as much of the information present in the sediment core data while generating as few artifacts in the interpolated field as possible. Based on a set of oxygen isotope ratios, we discuss several standard interpolation strategies, namely nearest neighbour schemes, bicubic splines, Delaunay triangulation, and ordinary and indicator kriging. We assess the gridded fields with regard to their physical consistence and their implications for the oceanic circulation

Analogue Gravity and ultrashort laser pulse filamentation

Ultrashort laser pulse filaments in dispersive nonlinear Kerr media induce a moving refractive index perturbation which modifies the space-time geometry as seen by co-propagating light rays. We study the analogue geometry induced by the filament and show that one of the most evident features of filamentation, namely conical emission, may be precisely reconstructed from the geodesics. We highlight the existence of favorable conditions for the study of analogue black hole kinematics and Hawking type radiation.Comment: 4 pages, revised versio

Quantum radiation from superluminal refractive index perturbations

We analyze in detail photon production induced by a superluminal refractive index perturbation in realistic experimental operating conditions. The interaction between the refractive index perturbation and the quantum vacuum fluctuations of the electromagnetic field leads to the production of photon pairs.Comment: 4 page

Spacetime geometries and light trapping in travelling refractive index perturbations

In the framework of transformation optics, we show that the propagation of a locally superluminal refractive index perturbation (RIP) in a Kerr medium can be described, in the eikonal approximation, by means of a stationary metric, which we prove to be of Gordon type. Under suitable hypotheses on the RIP, we obtain a stationary but not static metric, which is characterized by an ergosphere and by a peculiar behaviour of the geodesics, which are studied numerically, also accounting for material dispersion. Finally, the equation to be satisfied by an event horizon is also displayed and briefly discussed.Comment: 14 pages, 7 figure

Frizzled receptor 6 marks rare, highly tumourigenic stem-like cells in mouse and human neuroblastomas

Copyright © 2011 Cantilena et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The article was made available through the Brunel Open Access Publishing Fund.Wnt signalling is an important component of vertebrate development, required for specification of the neural crest. Ten Wnt receptors [Frizzled receptor 1-10 (Fzd1-10)] have been identified so far, some of which are expressed in the developing nervous system and the neural crest. Here we show that expression of one such receptors, Fzd6, predicts poor survival in neuroblastoma patients and marks rare, HIF1/2 α-positive cells in tumour hypoxic areas. Fzd6 positive neuroblastoma cells form neurospheres with high efficiency, are resistant to doxorubicin killing and express high levels of mesenchymal markers such as Twist1 and Notch1. Expression of Fzd6 is required for the expression of genes of the noncanonical Wnt pathway and the spheres forming activity. When transplanted into immunodeficient mice, neuroblastoma cells expressing the Fzd6 marker grow more aggressively than their Fzd6 negative counterparts. We conclude that Fzd6 is a new surface marker of aggressive neuroblastoma cells with stem cell-like features.This work was sponsored by the Wellcome Trust, the RICC cancer fund, SPARKS, the Italian Association for Cancer Research, Regione Liguria and the Italian Ministry of Health