Compensated Current Injection circuit, theory and applications

This paper presents a detailed description, analysis and example of practical application of a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops. This feature allows compensation for parasitic impedance connected in parallel with the useful load, which in turn keeps an excitation current flowing through the useful load independent of its impedance. The simplicity of the circuit and its good electrical properties are additional advantages of the scheme.Comment: 9 pages and 7 figures in one PDF fil

Finite-Size Effects on Return Interval Distributions for Weakest-Link-Scaling Systems

The Weibull distribution is a commonly used model for the strength of brittle materials and earthquake return intervals. Deviations from Weibull scaling, however, have been observed in earthquake return intervals and in the fracture strength of quasi-brittle materials. We investigate weakest-link scaling in finite-size systems and deviations of empirical return interval distributions from the Weibull distribution function. We use the ansatz that the survival probability function of a system with complex interactions among its units can be expressed as the product of the survival probability functions for an ensemble of representative volume elements (RVEs). We show that if the system comprises a finite number of RVEs, it obeys the $\kappa$-Weibull distribution. We conduct statistical analysis of experimental data and simulations that show good agreement with the $\kappa$-Weibull distribution. We show the following: (1) The weakest-link theory for finite-size systems involves the $\kappa$-Weibull distribution. (2) The power-law decline of the $\kappa$-Weibull upper tail can explain deviations from the Weibull scaling observed in return interval data. (3) The hazard rate function of the $\kappa$-Weibull distribution decreases linearly after a waiting time $\tau_c \propto n^{1/m}$, where $m$ is the Weibull modulus and $n$ is the system size in terms of representative volume elements. (4) The $\kappa$-Weibull provides competitive fits to the return interval distributions of seismic data and of avalanches in a fiber bundle model. In conclusion, using theoretical and statistical analysis of real and simulated data, we show that the $\kappa$-Weibull distribution is a useful model for extreme-event return intervals in finite-size systems.Comment: 33 pages, 11 figure

A percolation transition in Yang-Mills matter at finite number of colours

We examine baryonic matter at quark chemical potential of the order of the confinement scale, \mu_q\sim \lqcd. In this regime, quarks are supposed to be confined but baryons are close to the ``tightly packed limit'' where they nearly overlap in configuration space. We show that this system will exhibit a percolation phase transition {\em when varied in the number of colours} $N_c$: at high $N_c$, large distance correlations at quark level are possible even if the quarks are essentially confined. At low $N_c$, this does not happen. We discuss the relevance of this for dense nuclear matter, and argue that our results suggest a new ``phase transition'', varying $N_c$ at constant $\mu_q$.Comment: Accepted for publication, Physical Review Letters. Title changed from original, "Quarkyonic percolation at finite number of colors", at the request of the edito

Primary commodity prices: co-movements, common factors and fundamentals

The behavior of commodities is critical for developing and developed countries alike. This paper contributes to the empirical evidence on the co-movement and determinants of commodity prices. Using nonstationary panel methods, we document a statistically significant degree of co-movement due to a common factor. Within a Factor Augmented VAR approach, real interest rate and uncertainty, as postulated by a simple asset pricing model, are both found to be negatively related to this common factor. This evidence is robust to the inclusion of demand and supply shocks, which both positively impact on the co-movement of commodity prices.Commodity Prices, Panel Estimation, Factor Models

The Global Side of the Investments-Savings Puzzle

In this paper we re-examine the long standing and puzzling correlation between national savings and investment in industrial countries. We apply an econometric methodology that allows us to separate idiosyncratic correlation at the country level from correlation at the global level. In a major break with the existing literature, we find no evidence of a long run relationship in the idiosyncratic components of savings and investment. We also find that the global components in savings and investments commove, indicating that they react to shocks of a global nature.Savings, Investment, Feldstein-Horioka Puzzle, Panel Nonstationarity, Principal Components.

Interest Rate Co-movements, Global Factors and the Long End of the Term Spread

The disconnect between rising short and low long interest rates has been a distinctive feature of the 2000s. Both research and policy circles have argued that international forces, such as global monetary policy (e.g. Rogoff, 2006); international business cycles (e.g. Borio and Filardo, 2007); or a global savings glut (e.g Bernanke, 2005) may be responsible. In this paper, we employ recent advances in panel data econometrics to document the disconnect and link it explicitly to the existence of a global latent factor that dominates the long end of the term spread for the recent period; the saving glut story emerges as the most likely contender for the global factor.Short and Long Interest Rates, Financial Globalization, Panel Data, Factor Models

Scaling of v2v_2 in heavy ion collisions

We interpret the scaling of the corrected elliptic flow parameter w.r.t. the corrected multiplicity, observed to hold in heavy ion collisions for a wide variety of energies and system sizes. We use dimensional analysis and power-counting arguments to place constraints on the changes of initial conditions in systems with different center of mass energy $\sqrt{s}$. Specifically, we show that a large class of changes in the (initial) equation of state, mean free path, and longitudinal geometry over the observed $\sqrt{s}$ are likely to spoil the scaling in $v_2$ observed experimentally. We therefore argue that the system produced at most Super Proton Synchrotron (SPS) and Relativistic Heavy Ion Collider (RHIC) energies is fundamentally the same as far as the soft and approximately thermalized degrees of freedom are considered. The ``sQGP'' (Strongly interacting Quark-Gluon Plasma) phase, if it is there, is therefore not exclusive to RHIC. We suggest, as a goal for further low-energy heavy ion experiments, to search for a ``transition'' $\sqrt{s}$ where the observed scaling breaks.Comment: Accepted for publication by Phys. Rev. C Based on presentation in mini-symposium on QGP collective properties, Frankfurt. Discussion expanded, results adde

Domestic vs. International Correlations of Interest Rate Maturities

The association between long and short interest rates is traditionally envisaged from a purely domestic perspective, where it is believed an empirical regularity. Hence, the weakening of this relationship in the first half of the 2000s has represented a conundrum, calling for a reassessment of the term structure and the conduct of monetary policy. Some commentators have called for investigations into the international dimension of this puzzle. Hence, in this paper we employ recent advances in panel data econometrics to investigate the co-movement of interest rate maturities both at the domestic and international levels for a sample of industrial countries. Specifically, we use the Ng (2006) spacings correlations approach to examine interest rates correlations between and within countries. Compared to alternatives, this method does not just estimate bivariate correlations, but also assesses the degree of panel correlation without being restricted by the assumption of either zero or complete panel correlation. We find very small correlations between the different maturities of domestic rates and much higher correlations of international rates. Moreover, international correlations between long rates are significantly higher than those between short rates. These findings suggest a scenario for national monetary policy, where financial globalization may have changed the transmission mechanism, advocating searches for the “missing” yield curve in its international dimension.Financial globalization, yield spread, interest rates, spacings correlations