Condensate growth in trapped Bose gases

We study the dynamics of condensate formation in an inhomogeneous trapped Bose gas with a positive interatomic scattering length. We take into account both the nonequilibrium kinetics of the thermal cloud and the Hartree-Fock mean-field effects in the condensed and the noncondensed parts of the gas. Our growth equations are solved numerically by assuming that the thermal component behaves ergodically and that the condensate, treated within the Thomas-Fermi approximation, grows adiabatically. Our simulations are in good qualitative agreement with experiment, however important discrepancies concerning details of the growth behaviour remain.Comment: 28 pages, 11 figures. Changes made to the introduction, Sec. VI, Sec. VII, and included additional growth curves in Fig. 1

Phase separation on a hyperbolic lattice

We report a preliminary numerical study by kinetic Monte Carlo simulation of the dynamics of phase separation following a quench from high to low temperature in a system with a single, conserved, scalar order parameter (a kinetic Ising ferromagnet) confined to a hyperbolic lattice. The results are compared with simulations of the same system on two different, Euclidean lattices, in which cases we observe power-law domain growth with an exponent near the theoretically known value of 1/3. For the hyperbolic lattice we observe much slower domain growth, consistent to within our current accuracy with power-law growth with a much smaller exponent near 0.13. The paper also includes a brief introduction to non-Euclidean lattices and their mapping to the Euclidean plane.Comment: Computer Simulation Studies in Condensed Matter Physics 26 (CSP13), Edited by D.P. Landau, S.P. Lewis, H.-B. Schuttle

INSTITUTIONAL CHANGE AND ECONOMIC TRANSFORMATION IN BRAZIL, 1945-2004 - FROM INDUSTRIAL CATCHING-UP TO FINANCIAL FRAGILITY

This paper tries to explain the dynamics of Brazilian industrial catch-up in the last 60 years by discussing its background institutional conditions as well as its main macroeconomic features. After a brief introduction, the second section describes how after the institutional innovations introduced during the Vargas's and Kubitschek's administrations, a Brazilian version of the Developmental State was created, releasing the growth potential of the economy during the 1950s. The third section analyses the inflationary crisis and institutional inertia of the mid-1960s, and its solution through the introduction of a new of wave of institutional innovations and conflict management devices, which lead to the Brazilian growth miracle, until the debt crisis of early 1980s signaled its end. The fourth section analyses why the financial crisis, coupled with ineffective institutional changes and unsuccessful macroeconomic stabilization plans lead growth to a halt. It also includes an analysis of the pro-market reforms from the early 1990s onwards. The fifth section concludes the paper offering a brief sketch on how the analytical narrative fits the conceptual framework within which it was carried.

Knowledge technology and economic growth: recent evidence from OECD countries

This paper discusses some of the recent developments in growth theory, doing so from the perspective of a small open economy. After setting out a basic generic model, we show how it may yield two of the key models that have played a prominent role in the recent literature, the endogenous growth model and the non-scale growth model. We focus initially on the former, emphasizing how the simplest such model leads to an equilibrium in which the economy is always on its balanced growth path. One aspect of the model is the importance of fiscal policy as a determinant of the equilibrium growth rate, an aspect that is discussed in detail. We also show how the endogeneity or otherwise of the labor supply is crucial in determining the equilibrium growth rate and its responsiveness to macroeconomic policy. But transitional dynamics are an important aspect of the growth process and indeed much research has been directed to determining the speed with which the economy converges to its balanced growth path. We discuss alternative ways that such transitional dynamics may be introduced. These include (i) restricted access to the world capital market; (ii) the introduction of government capital , and (iii) the two-sector production model, pioneered by Lucas. In the original analysis, the two capital goods relate to physical and human capital and in the international context these naturally can be identified with traded and nontraded capital, respectively. Criticism of the endogenous growth model has led to the development of the nonscale growth model. This too is characterized by transitional dynamics, which are more flexible than those of the corresponding endogenous growth model. This model is much closer to the neoclassical model; in particular, the long-run growth rate is independent of macroeconomic policy. However, since such models are typically associated with slow convergence speeds, policy can influence the accumulation of capital for extended periods of time, leading to significant long-run level effects. The discussion seeks to emphasize the adaptability of the models to a wide range of issues. A final extension addresses the impact of volatililty on growth. This has been extensively analyzed empirically and a stochastic extension of the endogenous growth model provides a convenient framework within which to interpret this research.

The effects of distributed life cycles on the dynamics of viral infections

We explore the role of cellular life cycles for viruses and host cells in an infection process. For this purpose, we derive a generalized version of the basic model of virus dynamics (Nowak, M.A., Bangham, C.R.M., 1996. Population dynamics of immune responses to persistent viruses. Science 272, 74-79) from a mesoscopic description. In its final form the model can be written as a set of Volterra integrodifferential equations. We consider the role of age-distributed delays for death times and the intracellular (eclipse) phase. These processes are implemented by means of probability distribution functions. The basic reproductive ratio $R_0$ of the infection is properly defined in terms of such distributions by using an analysis of the equilibrium states and their stability. It is concluded that the introduction of distributed delays can strongly modify both the value of $R_0$ and the predictions for the virus loads, so the effects on the infection dynamics are of major importance. We also show how the model presented here can be applied to some simple situations where direct comparison with experiments is possible. Specifically, phage-bacteria interactions are analysed. The dynamics of the eclipse phase for phages is characterized analytically, which allows us to compare the performance of three different fittings proposed before for the one-step growth curve

Growth Effects of non Proprietary Innovation

We study an endogenous growth model where a profit-motivated R and D sector coexists with the introduction of free blueprints invented by philanthropists. These goods are priced at marginal cost, contrary to proprietary ones which are produced by a monopoly owned by the inventor. We show that philanthropy does not necessarily increase long-run growth and that it may even reduce welfare. The reason is that it crowds out proprietary innovation which on net may reduce total innovation in the long run. These effects would be reinforced if philanthropical innovation diverted people from other productive acitvities, if free goods were less tailored to customers than proprietary ones, and if philanthropical inventors sometimes came out with another version of an existing proprietary good. Dynamics can also be characterized and it is shown that the impact effect of free inventions on growth is positive.innovation, R&D, growth, open source, philanthropy, monopoly, imperfect competition, software industry