High-Dimensional Inference with the generalized Hopfield Model: Principal Component Analysis and Corrections

We consider the problem of inferring the interactions between a set of N binary variables from the knowledge of their frequencies and pairwise correlations. The inference framework is based on the Hopfield model, a special case of the Ising model where the interaction matrix is defined through a set of patterns in the variable space, and is of rank much smaller than N. We show that Maximum Lik elihood inference is deeply related to Principal Component Analysis when the amp litude of the pattern components, xi, is negligible compared to N^1/2. Using techniques from statistical mechanics, we calculate the corrections to the patterns to the first order in xi/N^1/2. We stress that it is important to generalize the Hopfield model and include both attractive and repulsive patterns, to correctly infer networks with sparse and strong interactions. We present a simple geometrical criterion to decide how many attractive and repulsive patterns should be considered as a function of the sampling noise. We moreover discuss how many sampled configurations are required for a good inference, as a function of the system size, N and of the amplitude, xi. The inference approach is illustrated on synthetic and biological data.Comment: Physical Review E: Statistical, Nonlinear, and Soft Matter Physics (2011) to appea

Low energy neutrino scattering measurements at future Spallation Source facilities

In the future several Spallation Source facilities will be available worldwide. Spallation Sources produce large amount of neutrinos from decay-at-rest muons and thus can be well adapted to accommodate state-of-the-art neutrino experiments. In this paper low energy neutrino scattering experiments that can be performed at such facilities are reviewed. Estimation of expected event rates are given for several nuclei, electrons and protons at a detector located close to the source. A neutrino program at Spallation Sources comprises neutrino-nucleus cross section measurements relevant for neutrino and core-collapse supernova physics, electroweak tests and lepton-flavor violation searches.Comment: 12 pages, 4 figures, 5 table

Concentration of Random-Coding Error Exponents

This paper studies the error exponent of i.i.d. randomly generated codes used for transmission over discrete memoryless channels with maximum likelihood decoding. Specifically, this paper shows that the error exponent of a code, defined as the negative normalized logarithm of the probability of error, converges in probability to the typical error exponent. For high rates, the result is a consequence of the fact that the random-coding error exponent and the sphere-packing error exponent coincide. For low rates, instead, the proof of convergence is based on the fact that the union bound accurately characterizes the probability of error

INTEGRAL observation of 3EG J1736-2908

The possible identification by INTEGRAL of the EGRET source 3EG J1736-2908 with the active galactic nucleus GRS 1734-292 is discussed. The latter was discovered in 1990 and later identified with a Seyfert 1 galaxy. At the time of the compilation of the 3rd EGRET Catalog, it was not considered as a possible counterpart of the source 3EG J1736-2908, which remained unidentified. A detailed multiwavelength study of the EGRET error circle is presented, by including archival radio, soft- and hard-X observations, suggesting that GRS 1734-292 could be a likely counterpart of 3EG J1736-2908, even though this poses very interesting questions about the production mechanisms of gamma-rays with energies greater than 100 MeV.Comment: 6 pages, 3 figures. Accepted for publication on A&A Main Journa

Bioethics aspects in the administration of clinical information by students of Dentistry

Objetivo: Evaluar el proceso de construcción de competencias vinculadas con la formación bioética. Métodos: Se realizó un estudio observacional descriptivo sobre variables: “aspectos legales de la información clínica” y “implementación del derecho a la información clínica”. Se registró una encuesta cerrada, voluntaria, anónima a una muestra azarosa de 300 estudiantes avanzados de la Carrera de Odontología de la FOUNLP, Argentina. El muestreo comprendió 150 alumnos de cuarto año (Grupo A) y 150 de quinto año (Grupo B). Los análisis estadísticos fueron realizados con Epi Info ™ Versión 3.3.2 y EPIDAT 3.1.Facultad de Odontologí

Unifying thermodynamic and kinetic descriptions of single-molecule processes: RNA unfolding under tension

We use mesoscopic non-equilibrium thermodynamics theory to describe RNA unfolding under tension. The theory introduces reaction coordinates, characterizing a continuum of states for each bond in the molecule. The unfolding considered is so slow that one can assume local equilibrium in the space of the reaction coordinates. In the quasi-stationary limit of high sequential barriers, our theory yields the master equation of a recently proposed sequential-step model. Non-linear switching kinetics is found between open and closed states. Our theory unifies the thermodynamic and kinetic descriptions and offers a systematic procedure to characterize the dynamics of the unfolding processComment: 13 pages, 3 figure

Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet

The electronic structure of the single molecule magnet system M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission spectroscopy, and density functional calculations. There is good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 eV and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron atom, giving a high spin state molecule with a total S=5 effective spin for the case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy

Inference of kinetic Ising model on sparse graphs

Based on dynamical cavity method, we propose an approach to the inference of kinetic Ising model, which asks to reconstruct couplings and external fields from given time-dependent output of original system. Our approach gives an exact result on tree graphs and a good approximation on sparse graphs, it can be seen as an extension of Belief Propagation inference of static Ising model to kinetic Ising model. While existing mean field methods to the kinetic Ising inference e.g., na\" ive mean-field, TAP equation and simply mean-field, use approximations which calculate magnetizations and correlations at time $t$ from statistics of data at time $t-1$, dynamical cavity method can use statistics of data at times earlier than $t-1$ to capture more correlations at different time steps. Extensive numerical experiments show that our inference method is superior to existing mean-field approaches on diluted networks.Comment: 9 pages, 3 figures, comments are welcom