General U(N) gauge transformations in the realm of covariant Hamiltonian field theory

A consistent, local coordinate formulation of covariant Hamiltonian field theory is presented. While the covariant canonical field equations are equivalent to the Euler-Lagrange field equations, the covariant canonical transformation theory offers more general means for defining mappings that preserve the action functional - and hence the form of the field equations - than the usual Lagrangian description. Similar to the well-known canonical transformation theory of point dynamics, the canonical transformation rules for fields are derived from generating functions. As an interesting example, we work out the generating function of type F_2 of a general local U(N) gauge transformation and thus derive the most general form of a Hamiltonian density that is form-invariant under local U(N) gauge transformations.Comment: 36 pages, Symposium on Exciting Physics: Quarks and gluons/atomic nuclei/biological systems/networks, Makutsi Safari Farm, South Africa, 13-20 November 2011; Exciting Interdisciplinary Physics, Walter Greiner, Ed., FIAS Interdisciplinary Science Series, Springer International Publishing Switzerland, 201

Essays on Dynamic Macroeconomics

The macroeconomic theory of optimal fiscal and monetary policy based on the assumption of a ‘benevolent dictator’ has identified several key lessons which are thought to substantially improve the economic conditions of a nation (see Chari and Kehoe, 1999, Woodford, 2003): (i) Debt should be zero or negative in the long run, (ii) taxes on capital income should be zero in the long run or on average, and (iii) in the analysis of monetary policy, fiscal policy can largely be neglected. However, due to either distortions in the political process or market frictions beyond reach of policymakers, these optimal, welfare-enhancing policies are often not implemented as recommended by economic theory. The aim of this thesis is therefore twofold: First, to explain the gap between recommended and actually implemented policies and, second, to find mechanisms (or alternative policies) aimed at attenuating these deviations from optimality. Chapter 2 studieswelfare consequences of a soft borrowing constraint on sovereign debt which is modeled as a proportional fine per unit of debt exceeding some reference value. Debt is the result of myopic fiscal policy where the government is assumed to have a smaller discount factor than the private sector. In the absence of lump-sum taxation, debt reduces welfare. The chapter shows that the imposition of the soft borrowing constraint, which resembles features of the Stability and Growth Pact and which is taken into account by the policy maker when setting its instruments, prevents excessive borrowing. The constraint can be implemented such as to (i) control the long run level of debt, (ii) prevent debt accumulation, and (iii) induce debt consolidation. In all three cases the constraint enhances welfare and these gains outweigh the short run welfare losses of increasing the costs of using debt to smooth taxes over the business cycle by two orders of magnitude. Why do governments tax capital in face of the benchmark of standard economic theory that capital ought to be untaxed? Chapter 3 provides a model of fiscal policy with endogenous labour, bonds, and capital in order to account for the observation that worldwide taxes on capital remain far from zero. It introduces policy myopia into an otherwise standard framework of optimal fiscal policy where the government can tax labour and capital income and shows, analytically for the case of quasi-linear preferences and numerically for the case of CRRA preferences, that policy myopia leads to empirically realistic tax rates on capital. Moreover, it is shown that the tax rate on capital increases as myopia increases. Finally, the chapter analyzes the effects of policy myopia on the conduct of fiscal policy over the business cycle. Based on the theoretical analysis of Chapter 3, Chapter 4 presents empirical support for the hypothesis that higher political instability leads to an increase of the tax rate on capital income. The hypothesis is tested on a panel of annual observations for 13 OECD countries for the period 1964-1983. Themain finding is that an increase of the index of political instability by one standard deviation leads to an increase of the tax rate on capital by about 1.8 percentage points. This effect is statistically and economically significant and robust against alternative sets of regressors and measures of the dependent variable, outlier correction, and alternative estimation strategies. Chapter 5 (joint with Markus Kirchner) assesses the role of sovereign risk in explaining macroeconomic fluctuations in Turkey. We estimate two versions of a simple New Keynesian small open economy model on quarterly data for the period 1994Q3-2008Q2: A basic version and a version augmented by a default premium on government debt due to a perceived risk of sovereign debt default. Model comparisons clearly support the augmented version since it leads to stronger internal propagation and hence smaller shocks are required in order to reconcile the observed dynamics of nominal and real variables, leading to better forecasting performance. The results suggest that the augmented model may lead to a better understanding of macroeconomic fluctuations in emerging market economies that are subject to sovereign risk. In terms of policy implications, counterfactual experiments show that both more active monetary policy and stronger fiscal feedbacks from debt on taxes can lead to less volatile inflation and debt dynamics, but higher debt feedbacks on taxation additionally reduce expected default rates

Mechanical and microstructural investigations of tungsten and doped tungsten materials produced via powder injection molding

The physical properties of tungsten such as the high melting point of 3420°C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate make this material attractive as a plasma facing material. However, the manufacturing of such tungsten parts by mechanical machining such as milling and turning is extremely costly and time intensive because this material is very hard and brittle. Powder Injection Molding (PIM) as special process allows the mass production of components, the joining of different materials without brazing and the creation of composite and prototype materials, and is an ideal tool for scientific investigations. This contribution describes the characterization and analyses of prototype materials produced via PIM. The investigation of the pure tungsten and oxide or carbide doped tungsten materials comprises the microstructure examination, element allocation, texture analyses, and mechanical testing via four-point bend (4-PB). Furthermore, the different materials were characterized by high heat flux (HHF) tests applying transient thermal loads at different base temperatures to address thermal shock and thermal fatigue performance. Additionally, HHF investigations provide information about the thermo-mechanical behavior to extreme steady state thermal loading and measurements of the thermal conductivity as well as oxidation tests were done. Post mortem analyses are performed quantifying and qualifying the occurring damage with respect to reference tungsten grades by metallographic and microscopical means

Post-Newtonian Freely Specifiable Initial Data for Binary Black Holes in Numerical Relativity

Construction of astrophysically realistic initial data remains a central problem when modelling the merger and eventual coalescence of binary black holes in numerical relativity. The objective of this paper is to provide astrophysically realistic freely specifiable initial data for binary black hole systems in numerical relativity, which are in agreement with post-Newtonian results. Following the approach taken by Blanchet, we propose a particular solution to the time-asymmetric constraint equations, which represent a system of two moving black holes, in the form of the standard conformal decomposition of the spatial metric and the extrinsic curvature. The solution for the spatial metric is given in symmetric tracefree form, as well as in Dirac coordinates. We show that the solution differs from the usual post-Newtonian metric up to the 2PN order by a coordinate transformation. In addition, the solutions, defined at every point of space, differ at second post-Newtonian order from the exact, conformally flat, Bowen-York solution of the constraints.Comment: 41 pages, no figures, accepted for publication in Phys. Rev. D, significant revision in presentation (including added references and corrected typos

The Loschmidt Echo as a robust decoherence quantifier for many-body systems

We employ the Loschmidt Echo, i.e. the signal recovered after the reversal of an evolution, to identify and quantify the processes contributing to decoherence. This procedure, which has been extensively used in single particle physics, is here employed in a spin ladder. The isolated chains have 1/2 spins with XY interaction and their excitations would sustain a one-body like propagation. One of them constitutes the controlled system S whose reversible dynamics is degraded by the weak coupling with the uncontrolled second chain, i.e. the environment E. The perturbative SE coupling is swept through arbitrary combinations of XY and Ising like interactions, that contain the standard Heisenberg and dipolar ones. Different time regimes are identified for the Loschmidt Echo dynamics in this perturbative configuration. In particular, the exponential decay scales as a Fermi golden rule, where the contributions of the different SE terms are individually evaluated and analyzed. Comparisons with previous analytical and numerical evaluations of decoherence based on the attenuation of specific interferences, show that the Loschmidt Echo is an advantageous decoherence quantifier at any time, regardless of the S internal dynamics.Comment: 12 pages, 6 figure

New insights into microstructure of neutron-irradiated tungsten

The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a great challenge. Tungsten is one of the promising candidate materials for plasma-facing components of future fusion reactors, due to several favorable properties as for example a high melting point, a high sputtering resistivity, and a low coefficient of thermal expansion. The microstructural details of a tungsten sample with a 1.25 dpa (displacements per atom) damage dose after neutron irradiation at 800 °C were examined by transmission electron microscopy. Three types of radiation-induced defects were observed, analyzed and characterized: (1) voids with sizes ranging from 10 to 65 nm, (2) dislocation loops with a size of up to 10 nm and (3) W–Re–Os containing σ- and χ-type precipitates. The distribution of voids as well as the nature of the occurring dislocation loops were studied in detail. In addition, nano-chemical analyses revealed that the σ- and χ-type precipitates, which are sometimes attached to voids, are surrounded by a solid solution cloud enriched with Re. For the first time the crystallographic orientation relationship of the σ- and χ-phases to the W-matrix was specified. Furthermore, electron energy-loss spectroscopy could not unambiguously verify the presence of He within individual voids

Untersuchungen über den Einfluß der Entsäuerung mit Calciumcarbonat auf die flüchtigen Inhaltsstoffe von Traubenmost und Wein

Investigations on the influence of deacidification with calciumcarbonate on the volatile constituents of grape must and wineChanges in the volatile constituents of musts and wines occurring during their chemical deacidification with calciumcarbonate were examined by use of GC-MS techniques. Owing to a change in pH, caused by CaC03 addition, an increase in the concentration of some monoterpenes, which are essential for the specific aroma of the varieties Morio-Muskat and Gewürztraminer, could be observed. This increase, concerning the monoterpene alcohols citronellol, nerol, geraniol and others, is due to the encymic hydrolysis of terpene glycosides present in must and wine