Fickle Investors: An Impediment to Growth?

The aim of this paper is to construct theoretical models which help to shed light on the recent criticisms of volatile investment flows. We do not make any empirical attempt to establish the existence or gauge the importance of the adverse effects of volatile investment flows nor do we make any implicit claims regarding the role of such flows in recent exchange rate crises. Instead we simply assume the existence of fickle outside investors and examine the consequences for the economy in the context of two partial equilibrium endogenous growth models. In our first model, the scale of fickle outside investment funds traces out a meanvariance tradeoff for the growth rate of the economy. In particular, the volatility of these funds dissuades risk averse agents from risky entrepreneural activities. This result opens up the possibility that some regulation of outside investment may increase growth. Our second model involves increasing returns and multiple equilibria. In the context of this model fickle investor behaviour can have very persistent and substantial effects on both output growth and volatility.growth;fickle investors;current account liberalization;volatility;Asian crisis;mean-variance tradeoff;multiple equilibria

Bayesian Reconstruction of Approximately Periodic Potentials at Finite Temperature

The paper discusses the reconstruction of potentials for quantum systems at finite temperatures from observational data. A nonparametric approach is developed, based on the framework of Bayesian statistics, to solve such inverse problems. Besides the specific model of quantum statistics giving the probability of observational data, a Bayesian approach is essentially based on "a priori" information available for the potential. Different possibilities to implement "a priori" information are discussed in detail, including hyperparameters, hyperfields, and non--Gaussian auxiliary fields. Special emphasis is put on the reconstruction of potentials with approximate periodicity. The feasibility of the approach is demonstrated for a numerical model.Comment: 18 pages, 17 figures, LaTe

Mean Field Methods for Atomic and Nuclear Reactions: The Link between Time--Dependent and Time--Independent Approaches

Three variants of mean field methods for atomic and nuclear reactions are compared with respect to both conception and applicability: The time--dependent Hartree--Fock method solves the equation of motion for a Hermitian density operator as initial value problem, with the colliding fragments in a continuum state of relative motion. With no specification of the final state, the method is restricted to inclusive reactions. The time--dependent mean field method, as developed by Kerman, Levit and Negele as well as by Reinhardt, calculates the density for specific transitions and thus applies to exclusive reactions. It uses the Hubbard--Stratonovich transformation to express the full time--development operator with two--body interactions as functional integral over one--body densities. In stationary phase approximation and with Slater determinants as initial and final states, it defines non--Hermitian, time--dependent mean field equations to be solved self--consistently as boundary value problem in time. The time--independent mean field method of Giraud and Nagarajan is based on a Schwinger--type variational principle for the resolvent. It leads to a set of inhomogeneous, non--Hermitian equations of Hartree--Fock type to be solved for given total energy. All information about initial and final channels is contained in the inhomogeneities, hence the method is designed for exclusive reactions. A direct link is established between the time--dependent and time--independent versions. Their relation is non--trivial due to the non--linear nature of mean field methods.Comment: 21 pages, to be published in European Physical Journal

Leptogenesis with exclusively low-energy CP Violation in the Context of Minimal Lepton Flavour Violation

We analyze lepton flavour violation (LFV) and the generation of the observed baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal lepton flavour violation framework with three quasi-degenerate heavy Majorana neutrinos. The BAU which is obtained through radiative resonant leptogenesis can successfully be generated widely independent of the Majorana scale in this scenario and flavour effects are found to be relevant. Then we discuss the specific case in which CP violation is exclusively present at low-energies (a real R matrix) in the flavour sensitive temperature regime. Successful leptogenesis in this case leads to strong constraints on low-energy neutrino parameters.Comment: Contrubution to the proceedings of the EPS HEP 2007 conference, Manchester (UK). 3 pages, 3 figure

Evolution of Directed Triangle Motifs in the Google+ OSN

Motifs are a fundamental building block and distinguishing feature of networks. While characteristic motif distribution have been found in many networks, very little is known today about the evolution of network motifs. This paper studies the most important motifs in social networks, triangles, and how directed triangle motifs change over time. Our chosen subject is one of the largest Online Social Networks, Google+. Google+ has two distinguishing features that make it particularly interesting: (1) it is a directed network, which yields a rich set of triangle motifs, and (2) it is a young and fast evolving network, whose role in the OSN space is still not fully understood. For the purpose of this study, we crawled the network over a time period of six weeks, collecting several snapshots. We find that some triangle types display significant dynamics, e.g., for some specific initial types, up to 20% of the instances evolve to other types. Due to the fast growth of the OSN in the observed time period, many new triangles emerge. We also observe that many triangles evolve into less-connected motifs (with less edges), suggesting that growth also comes with pruning. We complement the topological study by also considering publicly available user profile data (mostly geographic locations). The corresponding results shed some light on the semantics of the triangle motifs. Indeed, we find that users in more symmetric triangle motifs live closer together, indicating more personal relationships. In contrast, asymmetric links in motifs often point to faraway users with a high in-degree (celebrities)

On the chemical equilibration of strangeness-exchange reaction in heavy-ion collisions

The strangeness-exchange reaction pi + Y -> K- + N is shown to be the dynamical origin of chemical equilibration for K- production in heavy-ion collisions up to beam energies of 10 A GeV. The hyperons occurring in this process are produced associately with K+ in baryon-baryon and meson-baryon interactions. This connection is demonstrated by the ratio K-/K+ which does not vary with centrality and shows a linear correlation with the yield of pions per participant. At incident energies above AGS this correlation no longer holds due to the change in the production mechanism of kaons.Comment: 9 pages, 4 figure

A comprehensive study of rate capability in Multi-Wire Proportional Chambers

Systematic measurements on the rate capability of thin MWPCs operated in Xenon, Argon and Neon mixtures using CO2 as UV-quencher are presented. A good agreement between data and existing models has been found, allowing us to present the rate capability of MWPCs in a comprehensive way and ultimately connect it with the mobilities of the drifting ions.Comment: 29 pages, 18 figure