Direct application of UNIFAC activity coefficient computer programs to the calculation of solvent activities and .chi.-parameters for polymer solutions

Application of UNIFAC computer calculations to polymer solutions does not seem to make sense because of the value of the solvent activity: close to 1.000 over a considerable range of concentrations (up to 90% of polymer). A simple procedure is proposed to calculate solvent activity coefficients, and thus X-parameters, such that the easily available UNIFAC computer programs may be applied directly, without any modification

Charge Fluctuation in Heavy Ion Collisions

Charge fluctuations observed in early fixed-target proton-proton experiments are consistent with string models. In central heavy ion events the picture can change in two ways: strings can interact and find new ways to hadronize or they can be effectively inactivated to lose their dynamical role as ordering mechanism. Widely different charge fluctuations can be expected. The dispersion of the charges in a central rapidity box is an advantageous measure. In an explicit Dual-Parton-Model calculation using the DPMJET code and a randomized modification to simulated charge equilibrium, various energies and different nuclear sizes were considered. Local fluctuations were found to be a serious problem. However, for large enough detection regions charged particle fluctuations can provide a clear signal reflecting the basic dynamics of central heavy ion processes.Comment: 6 pages, 5 figures, Talk given at the Symposium on Multiparticle Dynamics, Alushta, Ukraine, Sept. 200

International benchmarking of South Africa's infrastructure performance

The paper provides a first systematic, comprehensive benchmarking of South Africa's infrastructure performance in four major sectors--electricity, water and sanitation, information and communication technology, and transportation--against the relevant group of comparator countries using a new World Bank international data base with objective and perception-based indicators of infrastructure performance from over 200 countries. Specifically, the paper seeks to answer a number of relevant questions: How does South Africa compare on major indicators of infrastructure sector performance against the relevant country groups? What do outcome indicators tell us about the relative strengths and weaknesses of South Africa's infrastructure compared with various income and geographical comparator groups of countries? Where are the largest deviations-positive and negative-from the benchmarks and other comparators? And how does one interpret some of these comparisons to be useful for policy purposes?Infrastructure Regulation,Economic Theory&Research,Income,Poverty Monitoring&Analysis,Economic Conditions and Volatility

Three-dimensional Self-similar Fractal Light in Canonical Resonators

Unstable canonical resonators can possess eigenmodes with a fractal intensity structure [Karman et al., Nature 402, 138(1999)]. In one particular transverse plane, the intensity is not merely statistically fractal, but self-similar [Courtial and Padgett, PRL 85, 5320 (2000)]. This can be explained using a combination of diffraction and imaging with magnification greater than one. Here we show that the same mechanism also shapes the intensity cross-section in the longitudinal direction into a self-similar fractal, but with a different magnification. This results in three-dimensional, self-similar, fractal intensity structure in the eigenmodes

Infrastructure and growth in South Africa : direct and indirect productivity impacts of 19 infrastructure measures

Empirical explorations of the growth and productivity impacts of infrastructure have been characterized by ambiguous (countervailing signs) results with little robustness. A number of explanations of the contradictory findings have been proposed. These range from the crowd-out of private by public sector investment, non-linearities generating the possibility of infrastructure overprovision, simultaneity between infrastructure provision and growth, and the possibility of multiple (hence indirect) channels of influence between infrastructure and productivity improvements. The authors explore these possibilities using panel data for South Africa over the 1970-2000 period, and a range of 19 infrastructure measures. Using a number of alternative measures of productivity, the prevalence of ambiguous (countervailing signs) results, with little systematic pattern is also shown to hold for their data set in estimations that include the infrastructure measures in simple growth frameworks.The authors demonstrate that controlling for potential endogeneity of infrastructure in estimation robustly eliminates virtually all evidence of ambiguous impacts of infrastructure, due for example to possible overinvestment in infrastructure. Controlling for the possibility of endogeneity in the infrastructure measures renders the impact of infrastructure capital not only positive, but of economically meaningful magnitudes. These findings are invariant between the direct impact of infrastructure on labor productivity, and the indirect impact of infrastructure on total factor productivity.Transport Economics Policy&Planning,Economic Theory&Research,Public Sector Economics&Finance,Economic Growth,Inequality

Forecasting investment needs in South Africa's electricity and telecommunications sectors

The authors use a panel-data set for the period 1980-2002 to estimate demand for electricity and telecommunications services and project investment needs in South Africa through 2010 for two growth scenarios. Projections of average annual investment needs in electricity and telecommunications for the current growth scenario (3.6 percent a year) are of the order of 0.2 percent and 0.75 percent of GDP, respectively. An alternative, accelerated growth scenario (6 percent a year) implies approximate doubling of investment needs in these sectors.Economic Theory&Research,Investment and Investment Climate,Banks&Banking Reform,Achieving Shared Growth,ICT Policy and Strategies

The structure of colloidosomes with tunable particle density: simulation vs experiment

Colloidosomes are created in the laboratory from a Pickering emulsion of water droplets in oil. The colloidosomes have approximately the same diameter and by choosing (hairy) particles of different diameters it is possible to control the particle density on the droplets. The experiment is performed at room temperature. The radial distribution function of the assembly of (primary) particles on the water droplet is measured in the laboratory and in a computer experiment of a fluid model of particles with pairwise interactions on the surface of a sphere.Comment: 16 pages, 2 tables, 7 figure