Spherical Hartree-Fock calculations with linear momentum projection before the variation.Part II: Spectral functions and spectroscopic factors

The hole--spectral functions and from these the spectroscopic factors have been calculated in an Galilei--invariant way for the ground state wave functions resulting from spherical Hartree--Fock calculations with projection onto zero total linear momentum before the variation for the nuclei 4He, 12C, 16O, 28Si, 32S and 40Ca. The results are compared to those of the conventional approach which uses the ground states resulting from usual spherical Hartree--Fock calculations subtracting the kinetic energy of the center of mass motion before the variation and to the results obtained analytically with oscillator occupations.Comment: 16 pages, 22 postscript figure

Spherical Hartree-Fock calculations with linear momentum projection before the variation.Part I: Energies, form factors, charge densities and mathematical sum rules

Spherical Hartree--Fock calculations with projection onto zero total linear momentum before the variation are performed for the nuclei 4He, 12C, 16O, 28Si, 32S and 40Ca using a density--independent effective nucleon--nucleon interaction. The results are compared to those of usual spherical Hartree--Fock calculations subtracting the kinetic energy of the center of mass motion either before or after the variation and to the results obtained analytically with oscillator occupations. Total energies, hole--energies, elastic charge form factors and charge densities and the mathematical Coulomb sum rules are discussed.Comment: 16 pages, 13 postscript figure

A Multi-Configuration Mixing Approach with Symmetry-Projected Complex Hartree-Fock-Bogoliubov Determinants

A multi-configuration mixing approach built on essentially complex, symmetry-projected Hartree-Fock-Bogoliubov (HFB) mean fields is introduced. The mean fields are obtained by variation after projection. The configuration space consists out of the symmetry-projected HFB vacuum and the symmetry-projected two-quasiparticle excitations for even, and the symmetry-projected one-quasiparticle excitations for odd A systems. The underlying complex HFB transformations are assumed to be time-reversal invariant and axially symmetric. The model allows nuclear structure calculations in large model spaces with arbitrary two-body interactions. The approach has been applied to $^{20}$Ne and $^{22}$Ne. Good agreement with the exact shell model results and considerable improvement with respect to older calculations, in which only real HFB transformations were admitted, is obtained.Comment: 30 pages LaTeX file, 4 Postscript figure

The Evolutionary Price of Anarchy: Locally Bounded Agents in a Dynamic Virus Game

The Price of Anarchy (PoA) is a well-established game-theoretic concept to shed light on coordination issues arising in open distributed systems. Leaving agents to selfishly optimize comes with the risk of ending up in sub-optimal states (in terms of performance and/or costs), compared to a centralized system design. However, the PoA relies on strong assumptions about agents\u27 rationality (e.g., resources and information) and interactions, whereas in many distributed systems agents interact locally with bounded resources. They do so repeatedly over time (in contrast to "one-shot games"), and their strategies may evolve. Using a more realistic evolutionary game model, this paper introduces a realized evolutionary Price of Anarchy (ePoA). The ePoA allows an exploration of equilibrium selection in dynamic distributed systems with multiple equilibria, based on local interactions of simple memoryless agents. Considering a fundamental game related to virus propagation on networks, we present analytical bounds on the ePoA in basic network topologies and for different strategy update dynamics. In particular, deriving stationary distributions of the stochastic evolutionary process, we find that the Nash equilibria are not always the most abundant states, and that different processes can feature significant off-equilibrium behavior, leading to a significantly higher ePoA compared to the PoA studied traditionally in the literature

Monetary targeting in practice : the German experience

From the mid-seventies on, the central banks of most major industrial countries switched to monetary targeting. The Bundesbank was the first central bank to take this step, making the switch at the end of 1974. This changeover to monetary targeting was due to the difficulties which the Bundesbank - like other central banks - was facing in pursuing its original strategy, and whichcame to a head in the early seventies, when inflation escalated. A second factor was the collapse of the Bretton Woods system of fixed exchange rates, which created the necessary scope for national monetary targeting. Finally, the advance of monetarist ideas fostered the explicit turn towards monetary targets, although the Bundesbank did not implement these in a mechanistic way. Whereas the Bundesbank has adhered to its policy of monetary targeting up to the present, nowadays monetary targeting plays only a minor role worldwide. Many central banks have switched to the strategy of direct inflation targeting. Others favour a more discretionary approach or a policy which is geared to the exchange rate. In the academic debate, monetary targeting is often presented as an outdated approach which has long since lost its basis of stable money demand. These findings give riseto a number of questions: Has monetary targeting actually become outdated? Which role is played by the concrete design of this strategy, and, against this background, how easily can it be transferred to European monetary union? This paper aims to answer these questions, drawing on the particular experience which the Bundesbank has gained of monetary targeting. It seems appropriate to discuss monetary targeting by using a specific example, since this notion is not very precise. This applies, for example, to the money definition used, the way the target is derived, the stringency applied in pursuing the target and the monetary management procedure

Compact Oblivious Routing

Oblivious routing is an attractive paradigm for large distributed systems in which centralized control and frequent reconfigurations are infeasible or undesired (e.g., costly). Over the last almost 20 years, much progress has been made in devising oblivious routing schemes that guarantee close to optimal load and also algorithms for constructing such schemes efficiently have been designed. However, a common drawback of existing oblivious routing schemes is that they are not compact: they require large routing tables (of polynomial size), which does not scale. This paper presents the first oblivious routing scheme which guarantees close to optimal load and is compact at the same time - requiring routing tables of polylogarithmic size. Our algorithm maintains the polylogarithmic competitive ratio of existing algorithms, and is hence particularly well-suited for emerging large-scale networks

A self consistent field approach to surfaces of compressible polymer blends

A self consistent field theory for compressible polymer mixtures is developed by introducing elements of classical density functional theory into the framework of the Helfand theory. It is then applied to study free surfaces of binary (A,B) polymer blends. Density profiles in the one- and two-phase region are calculated as well as chain end distributions and chain orientations of the minority and the majority component. In the ideally symmetric mixture, in which the individual properties of polymers A and B are the same and both have the same surface energy, polymers of the minority component segregate to the surface, where they are exposed to less polymers of the majority component. This effect can only be captured correctly, if one accounts for the fact that the monomer-monomer interaction has finite range. As a consequence, the Flory-Huggins-parameter varies in space and depends on the concentration profiles and their derivatives. The surface segregation calculated with such an ansatz, without any fit parameter, is in reasonable quantitative agreement with data from recent Monte Carlo simulations.Comment: 45 pages, latex, 12 figures, accepted by the Journal of Chemical physic