Development of an infinite input impedance fluidic amplifier

Two-phase analog infinite input impedance high stable gain fluid amplifie

Critical view of the claimed Θ+\Theta^+ pentaquark

We use a theoretical model of the $\gamma ~d \to ~K^+ K^- ~n ~p$ reaction adapted to the experiment done at LEPS where a peak was observed and associated to the $\Theta^{+}(1540)$ pentaquark. The study shows that the method used in the experiment to associate momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed $K^+ n$ invariant mass in the region of the claimed $\Theta^{+}(1540)$. It is shown that the LEPS fit to the data, used to make the claim of the $\Theta^{+}(1540)$, grossly distorts the background. An alternative fit, assuming a background plus a fluctuation, returns a background practically equal to the theoretical one and a fluctuation identical to the one seen in the experimental $K^- p$ spectrum of 2$\sigma$ significance.Comment: Conference Proceedin

An analytic Pade-motivated QCD coupling

We consider a modification of the Minimal Analytic (MA) coupling of Shirkov and Solovtsov. This modified MA (mMA) coupling reflects the desired analytic properties of the space-like observables. We show that an approximation by Dirac deltas of its discontinuity function $\rho$ is equivalent to a Pad\'e (rational) approximation of the mMA coupling that keeps its analytic structure. We propose a modification to mMA that, as preliminary results indicate, could be an improvement in the evaluation of low-energy observables compared with other analytic couplings.Comment: 2 pages, 1 figure (double), to appear in the Proceedings of the VIII Latin American Symposium on Nuclear Physics and Applications, Santiago, Chile, 15-19 December 2009. Poster presented by H. E. Martine

Automatic Generation of Cognitive Theories using Genetic Programming

Cognitive neuroscience is the branch of neuroscience that studies the neural mechanisms underpinning cognition and develops theories explaining them. Within cognitive neuroscience, computational neuroscience focuses on modeling behavior, using theories expressed as computer programs. Up to now, computational theories have been formulated by neuroscientists. In this paper, we present a new approach to theory development in neuroscience: the automatic generation and testing of cognitive theories using genetic programming. Our approach evolves from experimental data cognitive theories that explain “the mental program” that subjects use to solve a specific task. As an example, we have focused on a typical neuroscience experiment, the delayed-match-to-sample (DMTS) task. The main goal of our approach is to develop a tool that neuroscientists can use to develop better cognitive theories

Boxy/peanut bulges : formation, evolution and properties

We discuss the formation and evolution of boxy/peanut bulges (B/Ps) and present new simulations results. Orbital structure studies show that B/Ps are parts of bars seen edge-on, they have their origin in vertical instabilities of the disc material and they are somewhat shorter in extent than bars. When the bar forms it is vertically thin, but after a time of the order of a Gyr it experiences a vertical instability and buckles. At that time the strength of the bar decreases, its inner part becomes thicker, so that, seen edge-on, it acquires a peanut or boxy shape. A second buckling episode is seen in simulations with strong bars, accompanied by a further thickening of the B/P and a weakening of the bar. Quantitatively, this evolution depends considerably on the properties of the halo and particularly on the extent of its core. This influences the amount of angular momentum exchanged within the galaxy, emitted by near-resonant material in the bar region and absorbed by near-resonant material in the halo and in the outer disc. Haloes with small cores generally harbour stronger bars and B/Ps and they often witness double buckling.Comment: 7 pages, 3 figures, contribution to the conference "Chaos in Astronomy", Athens, sept. 2007, eds. G. Contopoulos & P.A. Patsi

Fermionic entanglement ambiguity in non-inertial frames

We analyse an ambiguity in previous works on entanglement of fermionic fields in non-inertial frames. This ambiguity, related to the anticommutation properties of field operators, leads to non-unique results when computing entanglement measures for the same state. We show that the ambiguity disappears when we introduce detectors, which are in any case necessary as a means to probe the field entanglement.Comment: 9 pages, 4 figures. Revtex 4.1, added Journal referenc