Invaded Cluster Dynamics for Frustrated Models

The Invaded Cluster (IC) dynamics introduced by Machta et al. [Phys. Rev. Lett. 75 2792 (1995)] is extended to the fully frustrated Ising model on a square lattice. The properties of the dynamics which exhibits numerical evidence of self-organized criticality are studied. The fluctuations in the IC dynamics are shown to be intrinsic of the algorithm and the fluctuation-dissipation theorem is no more valid. The relaxation time is found very short and does not present critical size dependence.Comment: notes and refernences added, some minor changes in text and fig.3,5,7 16 pages, Latex, 8 EPS figures, submitted to Phys. Rev.

Mixed signals: central bank independence, coordinated wage bargaining, and European Monetary Union

Plans for European Monetary Union are based on the conventional postulate that increasing the independence of the central bank can reduce inflation without any real economic effects. However, the theoretical and empirical bases for this claim rest onmodels of the economy that make unrealistic information assumptions and omitinstitutional variables other than the central bank. When the signaling problems between the central bank and other actors in the political economy are considered,we find that the character of wage bargaining conditions the impact of central bankindependence by rendering the signals between the bank and the bargainers moreor less effective. Greater independence can reduce inflation without majoremployment effects where bargaining is coordinated, but it brings higher levels ofunemployment where bargaining is uncoordinated. Thus, currency unions like the EMU may require higher levels of unemployment to control inflation than their proponents envisage; they will have costs as well as benefits, costs which will bedistributed unevenly among and within the member nations based on the changesinduced in the status of the bank and of wage coordination -- Die Konzepte für die Europäische Währungsunion basieren auf dem allgemeinvertretenen Postulat, daß mit größerer Unabhängigkeit der Zentralbank die Inflationohne reale ökonomische Effekte verringert werden kann. Allerdings beruht die theoretische wie empirische Basis für diesen Anspruch auf Modellvorstellungen einer Volkswirtschaft, die auf unrealistischen Annahmen der Bedeutung von Informationen beruhen und institutionelle Variable - mit Ausnahme der Zentralbank - außer acht lassen. Wird allerdings die wechselseitige Wahrnehmung und Interpretation vonInformationen (signaling problems) zwischen Zentralbank und den anderenAkteuren in der politischen Ökonomie in die Analyse einbezogen, dann ist festzustellen, daß die Art der Lohnfindung die Intensität der Auswirkungen derZentralbankunabhängigkeit beeinflußt je nachdem, wie wirksam die wechselseitige Wahrnehmung und Interpretation von Informationen zwischen der Zentralbank und den Tarifpartnern vermittelt ist.Im Falle koordinierter Tarifverhandlungen kann eine größere Unabhängigkeit derZentralbank die Inflation in der Tat ohne größere Beschäftigungseffekte vermindern,im Falle unkoordinierter Tarifverhandlungen führt dies allerdings zu einem höherenNiveau der Arbeitslosigkeit. Daraus leitet sich die Überlegung ab, daß eineWährungsunion vom Typ Europäische Währungsunion ein höheres Maß an Arbeitslosigkeit erfordert, um die Inflation unter Kontrolle zu halten, als es ihre Befürworter erwarten. Bei den sich dann einstellenden Vor- und Nachteilen werden die Nachteile zwischen und innerhalb der Mitgliedstaaten ungleich verteilt sein, abhängig von dem letztendlich verwirklichten Grad der Unabhängigkeit derZentralbank und der Form der Lohnfindung.

Modulation of the CD8+-T-cell response by CD4+ CD25+ regulatory T cells in patients with Hepatitis B virus infection

CD4+ CD25+ regulatory T cells have been shown to maintain peripheral tolerance against self and foreign antigens. In this study we analyzed the effect of circulating CD4+ CD25+ T cells on CD8+-T-cell responses of patients with chronic and resolved hepatitis B virus (HBV) infection. We demonstrated that circulating CD4+ CD25+ T cells modulate the function and expansion of HBV-specific CD8+ cells ex vivo in all patients, regardless of whether they have chronic or resolved HBV infection. The possible role of CD4+ CD25+ T cells in the pathogenesis of chronic HBV infection is not supported by these data. However, these results might have implications for optimizing future immunotherapeutic approaches to HBV treatment

Water-like hierarchy of anomalies in a continuous spherical shouldered potential

We investigate by molecular dynamics simulations a continuous isotropic core-softened potential with attractive well in three dimensions, introduced by Franzese [cond-mat/0703681, to appear on Journal of Molecular Liquids], that displays liquid-liquid coexistence with a critical point and water-like density anomaly. Here we find diffusion and structural anomalies. These anomalies occur with the same hierarchy that characterizes water. Yet our analysis shows differences with respect to the water case. Therefore, many of the anomalous features of water could be present in isotropic systems with soft-core attractive potentials, such as colloids or liquid metals, consistent with recent experiments showing polyamorphism in metallic glasses.Comment: 27 pages, 9 figures. to appear in J. Chem. Phy

Density anomaly in a competing interactions lattice gas model

We study a very simple model of a short-range attraction and an outer shell repulsion as a test system for demixing phase transition and density anomaly. The phase-diagram is obtained by applying mean field analysis and Monte Carlo simulations to a two dimensional lattice gas with nearest-neighbors attraction and next-nearest-neighbors repulsion (the outer shell). Two liquid phases and density anomaly are found. The coexistence line between these two liquid phases meets a critical line between the fluid and the low density liquid at a tricritical point. The line of maximum density emerges in the vicinity of the tricritical point, close to the demixing transition