Phase transition in the Countdown problem

Here we present a combinatorial decision problem, inspired by the celebrated quiz show called the countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We then derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit.Comment: Submitted for publicatio

The Visibility Graph: a new method for estimating the Hurst exponent of fractional Brownian motion

Fractional Brownian motion (fBm) has been used as a theoretical framework to study real time series appearing in diverse scientific fields. Because its intrinsic non-stationarity and long range dependence, its characterization via the Hurst parameter H requires sophisticated techniques that often yield ambiguous results. In this work we show that fBm series map into a scale free visibility graph whose degree distribution is a function of H. Concretely, it is shown that the exponent of the power law degree distribution depends linearly on H. This also applies to fractional Gaussian noises (fGn) and generic f^(-b) noises. Taking advantage of these facts, we propose a brand new methodology to quantify long range dependence in these series. Its reliability is confirmed with extensive numerical simulations and analytical developments. Finally, we illustrate this method quantifying the persistent behavior of human gait dynamics.Comment: 5 pages, submitted for publicatio

Risk and protective factors for release in outpatients with schizophrenia

eposterWe aim to determine risk and protective factors influencing relapse incidence in outpatient with schizophrenia. A longitudinal, observational study was done with outpatients with schizophrenia (F20) or schizoaffective disorder (F25)(DMS-IV and ICD-10), without hospitalization during the previous 6 months. The patients were consecutively included into the study to received oral (O-A) or long-acting injectable (depot-A) antipsychotics. Clinical stage evolution, compliance, efficacy and safety assessments (including PANSS, CGI-SSI, hospitalization rates, and adverse events) were recorded before and after 6 and 12 months of treatment. Results: 60 outpatients (aged 34.5±8.9, male 73%), 75% schizophrenia and 25% schizoaffective disorder diagnosis, 68.3% fewer than 15 years of schizophrenia evolution, 76.7% fewer than 5 times previous hospitalizations were treated with O-A (41.7%) or depot-A (58.3%) antipsychotics for at least one year. Depot-A treated patients showed a significant higher compliance compared to O-A patients during the all following time, lower PANSS (total, positive and negative) scores and CGI-SSI score (p<0.01), and a delayed relapse incidence and re-hospitalization to more than 1 year in the 48% of patients (relapse % depot/% oral) after 6 months 22.9%/52.0%, and after 12 months 48.6%/4.0%. Conclusion: There were protective factors which delayed relapse incidence in schizophrenia: Use of sustained-release preparations, family support. There were risk factors for occurrence of relapse in schizophrenia: cocaine, heroin and alcohol consumption, absence of family support, greater severity of patients assessed through CGI-SI, male sex, age older than 25 years and long-term evolution of the disorder.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Are gauge shocks really shocks?

The existence of gauge pathologies associated with the Bona-Masso family of generalized harmonic slicing conditions is proven for the case of simple 1+1 relativity. It is shown that these gauge pathologies are true shocks in the sense that the characteristic lines associated with the propagation of the gauge cross, which implies that the name ``gauge shock'' usually given to such pathologies is indeed correct. These gauge shocks are associated with places where the spatial hypersurfaces that determine the foliation of spacetime become non-smooth.Comment: 7 pages, 5 figures, REVTEX 4. Revised version, including corrections suggested by referee

Quality Testing of Gaseous Helium Pressure Vessels by Acoustic Emission

The resistance of pressure equipment is currently tested, before commissioning or at periodic maintenance, by means of normal pressure tests. Defects occurring inside materials during the execution of these tests or not seen by usual non-destructive techniques can remain as undetected potential sources of failure . The acoustic emission (AE) technique can detect and monitor the evolution of such failures. Industrial-size helium cryogenic systems employ cryogens often stored in gaseous form under pressure at ambient temperature. Standard initial and periodic pressure testing imposes operational constraints which other complementary testing methods, such as AE, could significantly alleviate. Recent reception testing of 250 m3 GHe storage vessels with a design pressure of 2.2 MPa for the LEP and LHC cryogenic systems has implemented AE with the above-mentioned aims

Morfología polínica de las especies de cítricos cultivadas en Andalucía occidental (España)

. Morfología polínica de las especies de cítricos cultivadas en Andalucía occidental (España). Se estudia la morfología polínica de seis especies de cítricos de los géneros Citrus (C. aurantium, C. deliciosa, C. grandis, C. limon y C. sinensis) y Fortunella (F. margarita), con los microscopios óptico y electrónico de barrido. Por los caracteres estudiados (polaridad, simetría, contorno (en visión ecuatorial y corte óptico meridiano y visión polar y corte ecuatorial), tamaño, número, tipo y dimensiones de las aberturas, grosor de la exina y ornamentación) se describe la morfología del polen y se discuten los resultados obtenidos.No es posible la separación de los dos géneros, pero se pueden diferenciar parte de las especies del género Citrus

The Partition Function of Multicomponent Log-Gases

We give an expression for the partition function of a one-dimensional log-gas comprised of particles of (possibly) different integer charge at inverse temperature {\beta} = 1 (restricted to the line in the presence of a neutralizing field) in terms of the Berezin integral of an associated non- homogeneous alternating tensor. This is the analog of the de Bruijn integral identities [3] (for {\beta} = 1 and {\beta} = 4) ensembles extended to multicomponent ensembles.Comment: 14 page

Predicción del rendimiento académico en las nuevas titulaciones de grado de la EPS de la Universidad de Córdoba

En este artículo se describe una experiencia de innovación docente que tiene como finalidad predecir el rendimiento académico de los estudiantes de primer curso de grado universitario utilizando técnicas de minería de datos. La investigación se ha realizado utilizando información de los alumnos de tres asignaturas de introducción a la informática que se han impartido durante el primer cuatrimestre del curso 2010-11 en las distintas titulaciones de grado de la Escuela Politécnica Superior de la Universidad de Córdoba.SUMMARY -- In this paper, we describe an educational innovation experience about the prediction of the students’ academic performance during the first year of university degree by applying data mining techniques. The research has been carried out by using the information of students of three subjects about introduction to computer science during the first semester of 2010-11 academic year in the different degrees of the Higher Technical College of the University of Cordoba.Peer Reviewe

Time series irreversibility: a visibility graph approach

We propose a method to measure real-valued time series irreversibility which combines two differ- ent tools: the horizontal visibility algorithm and the Kullback-Leibler divergence. This method maps a time series to a directed network according to a geometric criterion. The degree of irreversibility of the series is then estimated by the Kullback-Leibler divergence (i.e. the distinguishability) between the in and out degree distributions of the associated graph. The method is computationally effi- cient, does not require any ad hoc symbolization process, and naturally takes into account multiple scales. We find that the method correctly distinguishes between reversible and irreversible station- ary time series, including analytical and numerical studies of its performance for: (i) reversible stochastic processes (uncorrelated and Gaussian linearly correlated), (ii) irreversible stochastic pro- cesses (a discrete flashing ratchet in an asymmetric potential), (iii) reversible (conservative) and irreversible (dissipative) chaotic maps, and (iv) dissipative chaotic maps in the presence of noise. Two alternative graph functionals, the degree and the degree-degree distributions, can be used as the Kullback-Leibler divergence argument. The former is simpler and more intuitive and can be used as a benchmark, but in the case of an irreversible process with null net current, the degree-degree distribution has to be considered to identifiy the irreversible nature of the series.Comment: submitted for publicatio