Initial Condition for QGP Evolution from NEXUS

We recently proposed a new approach to high energy nuclear scattering, which treats the initial stage of heavy ion collisions in a sophisticated way. We are able to calculate macroscopic quantities like energy density and velocity flow at the end of this initial stage, after the two nuclei having penetrated each other. In other words, we provide the initial conditions for a macroscopic treatment of the second stage of the collision. We address in particular the question of how to incorporate the soft component properly. We find almost perfect "Bjorken scaling": the rapidity coincides with the space-time rapidity, whereas the transverse flow is practically zero. The distribution of the energy density in the transverse plane shows typically a very "bumpy" structure.Comment: 17 pages, 24 figure

Guided Interface Waves

Many of tomorrow’s technologies are dependent upon the emergence of new advanced materials with superior stiffness and strength but reduced density. Metal matrix composites (MMC’s) consisting of light metal matrices (e. g., aluminum, titanium or magnesium) reinforced with very stiff ceramic fibers or particles (e. g. SiC, AI2O3 or graphite) show considerable promise for satisfying this need. However, the satisfactory performance of these materials has been found to be critically dependent upon the attainment of optimal properties at the metal-ceramic interface; a problem that is compounded by the possibility of chemical reactions between the reactive metal matrix and ceramic reinforcement. Of particular import are the interface adhesion and local elastic properties. Unfortunately no methods exist for the measurement of these quantities even for macroscopic interfaces let alone for the microscopic interfaces occurring within MMC’s

Self-Consistency Requirement in High-Energy Nuclear Scattering

Practically all serious calculations of exclusive particle production in ultra-relativistic nuclear or hadronic interactions are performed in the framework of Gribov-Regge theory or the eikonalized parton model scheme. It is the purpose of this paper to point out serious inconsistencies in the above-mentioned approaches. We will demonstrate that requiring theoretical self-consistency reduces the freedom in modeling high energy nuclear scattering enormously. We will introduce a fully self-consistent formulation of the multiple-scattering scheme in the framework of a Gribov-Regge type effective theory. In addition, we develop new computational techniques which allow for the first time a satisfactory solution of the problem in the sense that calculation s of observable quantities can be done strictly within a self-consistent formalism.Comment: 7 pages, 6 figure

Cosmic Ray Air Shower Characteristics in the Framework of the Parton-Based Gribov-Regge Model NEXUS

The purpose of this paper is twofold: first we want to introduce a new type of hadronic interaction model (NEXUS), which has a much more solid theoretical basis as, for example, presently used models like QGSJET and VENUS, and ensures therefore a much more reliable extrapolation towards high energies. Secondly, we want to promote an extensive air shower (EAS) calculation scheme, based on cascade equations rather than explicit Monte Carlo simulations, which is very accurate in calculations of main EAS characteristics and extremely fast concerning computing time. We employ the NEXUS model to provide the necessary data on particle production in hadron-air collisions and present the average EAS characteristics for energies 10^14 - 10^17 eV. The experimental data of the casa-blanka group are analyzed in the framework of the new model.Comment: 15 pages, 8 figure

Enhanced Perturbative Continuous Unitary Transformations

Unitary transformations are an essential tool for the theoretical understanding of many systems by mapping them to simpler effective models. A systematically controlled variant to perform such a mapping is a perturbative continuous unitary transformation (pCUT) among others. So far, this approach required an equidistant unperturbed spectrum. Here, we pursue two goals: First, we extend its applicability to non-equidistant spectra with the particular focus on an efficient derivation of the differential flow equations, which define the enhanced perturbative continuous unitary transformation (epCUT). Second, we show that the numerical integration of the flow equations yields a robust scheme to extract data from the epCUT. The method is illustrated by the perturbation of the harmonic oscillator with a quartic term and of the two-leg spin ladders in the strong-rung-coupling limit for uniform and alternating rung couplings. The latter case provides an example of perturbation around a non-equidistant spectrum.Comment: 27 pages, 18 figures; separated methodological background from introduction, added perturbed harmonic oscillator for additional illustration, added explicit solution of deepCUT equation

Ultrasonic Methods for Characterizing the Interface in Composites

Micromechanical modeling studies of composite materials have highlighted the need for better characterization of the interface zone in composite materials. Bulk behavior in composites has been predicted to be strongly influenced by the local elastic properties, residual stresses, and adhesion of the interface. Techniques to nondestructively measure these newly perceived quantities of importance do not exist. Thus it is not possible experimentally to (i) confirm the micromechanical model predictions, (ii) explore the relationships between interface properties and processing variables, and (iii) ensure acceptable interface properties in commercially fabricated composites. We report here the current status of a SDIO/ONR funded research program directed at developing experimental techniques for characterizing the interface zone in composites through the use of ultrasonic interface waves [1]

On the Role of Energy Conservation in High-Energy Nuclear Scattering

We argue that most commonly used models for nuclear scattering at ultra-relativistic energies do not treat energy conservation in a consistent fashion. Demanding theoretical consistency as a minimal requirement for a realistic model, we provide a solution for the above-mentioned problem, the so-called ``Parton-Based Gribov-Regge Theory''. In order to keep a clean picture, we do not consider secondary interactions. We provide a very transparent extrapolation of the physics of more elementary interactions towards nucleus-nucleus scattering, without considering any nuclear effects due to final state interactions. In this sense we consider our model a realistic and consistent approach to describe the initial stage of nuclear collisions.Comment: 17 pages, LaTeX created with LyX, 10 figure

Policy brief, number 11, 2014

[From Introduction] Urbanisation in sub-Saharan Africa: changing the locus of poverty. Urbanisation is a global phenomenon that is changing the face of the Earth, as well as how people earn a living and secure their livelihoods. In 2006 the number of urban people in the world surpassed the number of rural people, and this gap will continue to grow. In only 16 years (by 2030) just under two-thirds of the world's people will be urban dwellers. Whilst most of the developed world and large parts of Latin America already have more than threequarters of their populations living in cities and towns, most countries in Asia and sub-Saharan Africa are still catching up. This means that they are experiencing massive migrations from rural to urban areas as rural people wish to swap the insecurities of rural living for the allure of secure employment and better services for health, education, sanitation and transport in towns and cities. Sub-Saharan Africa (SSA) is the most rapidly urbanising region of the globe. According to UN-Habitat, in 1990, only 28 % of the region's inhabitants lived in towns and cities; that increased to approximately 32 % in 2001 and 41 % in 2010. The size of the urban population is likely to surpass the rural one around 2025. Contrary to popular belief, most urban residents in SSA (and globally) live in small towns rather than massive megacities; with just over half living in towns of less than 200,000 people and 78 % living in towns of less than 500,000 residents. Only 14 % of urban dwellers live in cities of more than one million people. Many new urban households maintain strong links to relatives and clans in rural areas, with circular migration patterns emerging as the urban transition takes place over several decades. The implications of this extremely rapid urbanisation in SSA countries for livelihoods and poverty are widely debated. UN-Habitat highlights a relatively unique aspect of urbanisation in SSA as being the accompanying high rate of growth in informal settlements or slums. In other words, not all rural migrants to towns and cities find secure incomes or shelter. Some slum areas have become permanent features where inter-generational poverty is reproduced. Although urban areas are producing an increasing share of national wealth in SSA countries, some argue that slowly the nexus of poverty is shifting towards urban areas. Rates of poverty are high in rural areas of SSA, but migration and internal population growth means that in some countries the number of urban poor almost matches the number of rural poor, and it is likely to grow. The informal economy contributes an average of 40 – 45 % of total urban GDP, which is higher than any other region of the world