ATP as a presynaptic modulator

© 2000 Elsevier Science Inc.There is considerable evidence that ATP acts as a fast transmitter or co-transmitter in autonomic and sensory nerves mostly through activation of ionotropic P2X receptors but also through metabotropic P2Y receptors. By analogy, the observations that ATP is released from stimulated central nervous system (CNS) nerve terminals and that responses to exogenously added ATP can be recorded in central neurons, lead to the proposal that ATP might also be a fast transmitter in the CNS. However, in spite of the robust expression of P2 receptor mRNA and binding to P2 receptors in the CNS, the demonstration of central purinergic transmission has mostly remained elusive. We now review evidence to suggest that ATP may also act presynaptically rather than solely postsynaptically in the nervous system.Fundação Ciência e Tecnologia and European nio

Counting all cubes in {0,1,...,n}^3

In this paper we describe a procedure of calculating the number cubes that have coordinates in the set {0,1,...,n}. We adapt the code that appeared in [11] developed to calculate the number of regular tetrahedra with coordinates in the set {0,1,...,n}. The idea is based on the theoretical results obtained in [13]. We extend then the sequence A098928 in the Online Encyclopedia of Integer Sequences to the first one hundred terms.Comment: 24 pages, 5 figure

A non-linear transport method for detecting superconducting stripes

We theoretically study the effect of stripe-like superconducting inclusions on the non-linear resistivity in single crystals. Even when the stripe orientation varies throughout the sample between two orthogonal directions due to twinning, we predict that there should be a universal scaling relationship between the nonlinear resistivity curves measured at different angles relative to the crystal axes. This prediction can be used to verify or rule out the existence of superconducting stripes at and above the superconducting transition temperature in cuprate superconductors.Comment: 4 pages, 4 figure

On the determinants of the Chilean Economic Growth

This paper presents several methodologies for understanding the Chilean growth process. By using univariate time series representations, we find that the Chilean data is more consistent with exogenous than with endogenous growth models. Growth accounting exercises show that the mild growth rates of the sixties are mainly due to the accumulation of human and physical capital, while the booms of the mid seventies and the one from 1985 until 1998 are mainly due to TFP growth. We also find that among the most important determinants of the evolution of TFP are the evolution of terms of trade, improvements on the quality of capital, and the presence of distortions. In fact, distortions do not only eliminate the positive effects of improvements on the quality of capital, but also precede the evolution of technology shocks and increase their volatility. A dynamic stochastic general equilibrium model that explicitly incorporates the relative price of investment with respect to consumption goods, terms of tra de, and distortionary taxes is able to successfully replicate the impulse-response functions found on the data. This exercise suggests that distortions play a key role in explaining the growth dynamics of the Chilean experience.

Strong asymmetry for surface modes in nonlinear lattices with long-range coupling

We analyze the formation of localized surface modes on a nonlinear cubic waveguide array in the presence of exponentially-decreasing long-range interactions. We find that the long-range coupling induces a strong asymmetry between the focusing and defocusing cases for the topology of the surface modes and also for the minimum power needed to generate them. In particular, for the defocusing case, there is an upper power threshold for exciting staggered modes, which depends strongly on the long-range coupling strength. The power threshold for dynamical excitation of surface modes increase (decrease) with the strength of long-range coupling for the focusing (defocusing) cases. These effects seem to be generic for discrete lattices with long-range interactions.Comment: 4 pages, 5 figures, submitted for publicatio

Perspectives for the radiative return at meson factories

The measurement of the pion form factor and, more generally, of the cross section for electron-positron annihilation into hadrons through the radiative return has become an important task for high luminosity colliders such as the Phi- or B-meson factories. This quantity is crucial for predictions of the hadronic contributions to the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling. But the radiative return opens the possibility of many other physical applications. The physics potential of this method at high luminosity meson factories is discussed, the last upgraded version of the event generator PHOKHARA is presented, and future developments are highlighted.Comment: Presented at SIGHAD03: Worskhop on Hadronic Cross Section at Low Energy, Pisa,Italy, October 8th-10th, 200