Microcanonical Approach to the Simulation of First-Order Phase Transitions

A generalization of the microcanonical ensemble suggests a simple strategy for the simulation of first order phase transitions. At variance with flat-histogram methods, there is no iterative parameters optimization, nor long waits for tunneling between the ordered and the disordered phases. We test the method in the standard benchmark: the Q-states Potts model (Q=10 in 2 dimensions and Q=4 in 3 dimensions), where we develop a cluster algorithm. We obtain accurate results for systems with more than one million of spins, outperforming flat-histogram methods that handle up to tens of thousands of spins.Comment: 4 pages, 3 postscript figure

The Perverse Response of Interest Rates

We argue that an increase in aggregate demand can lead to a reduction in the interest rate. This apparently perverse optimal response of interest rates can occur when the Phillips curve is non-linear. In that case, an increase in aggregate demand tends to increase inflation and output but also to change the weight on inflation in the optimal monetary policy rule. Although the first two effects tend to increase interest rates, the latter effect can imply lower interest rates. If this effect dominates, interest rates can fall

Non-linear and non-symmetric exchange-rate adjustment: new evidence from medium and high inflation countries

This paper analyses a model of non-linear exchange rate adjustment that extends the literature by allowing asymmetric responses to over- and under-valuations. Applying the model to Greece and Turkey, we find that adjustment is asymmetric and that exchange rates depend on the sign as well as the magnitude of deviations, being more responsive to over-valuations than under-valuations. Our findings support and extend the argument that non-linear models of exchange rate adjustment can help to overcome anomalies in exchange rate behaviour. They also suggest that exchange rate adjustment is non-linear in economies where fundamentals models work well

Mean-value identities as an opportunity for Monte Carlo error reduction

In the Monte Carlo simulation of both Lattice field-theories and of models of Statistical Mechanics, identities verified by exact mean-values such as Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide well known and sensitive tests of thermalization bias as well as checks of pseudo random number generators. We point out that they can be further exploited as "control variates" to reduce statistical errors. The strategy is general, very simple, and almost costless in CPU time. The method is demonstrated in the two dimensional Ising model at criticality, where the CPU gain factor lies between 2 and 4.Comment: 10 pages, 2 tables. References updated and typos correcte

Phase boundary detection for dilution refrigerators

We describe a device to conveniently measure the positions of the phase boundaries in a dilution refrigerator. We show how a simple modification of a standard capacitive level gauge (segmentation of one of the electrodes) permits a direct calibration of the capacitance versus phase boundary position. We compare this direct calibration with the indirect procedure that must be adopted for a conventional capacitive level gauge. The device facilitates the correct adjustment of the 3He/4He fraction in the dilution refrigerator.Comment: 3 page

Synthesis and Characterization of platinum – selenium Derivatives: X-ray Structure of \u3cem\u3etrans\u3c/em\u3e-Pt(Pet\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3e(SePh)\u3csub\u3e2\u3c/sub\u3e

The crystal structure of trans-[((bis)triethylphosphine)(bis(phenylselenato))platinum (II)] has been determined by single crystal X-ray diffraction. Crystallization occurs in the triclinic space group P-1 (No. 2) with a = 8.9964(2) Å, b = 11.5103(2) Å, c = 14.9335(3) Å; α = 85.8750(10)°, β = 72.5350(10)°, γ = 68.4450(10)°. Details of the structure and spectroscopic results are presented and discussed and comparisons are made with related square planar platinum (II) structures