Non-convex image reconstruction via Expectation Propagation

Tomographic image reconstruction can be mapped to a problem of finding solutions to a large system of linear equations which maximize a function that includes \textit{a priori} knowledge regarding features of typical images such as smoothness or sharpness. This maximization can be performed with standard local optimization tools when the function is concave, but it is generally intractable for realistic priors, which are non-concave. We introduce a new method to reconstruct images obtained from Radon projections by using Expectation Propagation, which allows us to reframe the problem from an Bayesian inference perspective. We show, by means of extensive simulations, that, compared to state-of-the-art algorithms for this task, Expectation Propagation paired with very simple but non log-concave priors, is often able to reconstruct images up to a smaller error while using a lower amount of information per pixel. We provide estimates for the critical rate of information per pixel above which recovery is error-free by means of simulations on ensembles of phantom and real images.Comment: 12 pages, 6 figure

Generalizability Theory Applied to Olympic Male Taekwondo Combats

Generalizability theory (GT) postulates that there are infinite sources of error variation in any measurement. Generalizability analysis is used to reduce and control this measurement error. To date, there has been no study employing GT in analysing taekwondo, despite the increase of observational studies in combat sports. Through applying GT to six random combat bouts within the Olympic Games in London 2012, the aims of this study are: (a) to determine whether the bouts selected are representative enough for their behaviour to be generalizable; (b) to determine the intra and interobserver agreement and reliability; and (c) to assess the accuracy of the exhaustive and mutual exclusion of each category included in each criterion of the categorical system. Method: Six taekwondo bouts were randomly selected in order to analyse the athletes' technical/tactical behaviour. Three observers were responsible for viewing and analysing the videos using a consensual concordance strategy. Results and discussion: High values for intra and interobserver agreement were found in Kendall's tau and Cohen's kappa indexes, in addition to the GT. The results showed that the categorical system was composed of exhaustive and mutually exclusive (E/ME) categories and that the sample was representative enough to generalize the behaviour shown

Improving randomness characterization through Bayesian model selection

Nowadays random number generation plays an essential role in technology with important applications in areas ranging from cryptography, which lies at the core of current communication protocols, to Monte Carlo methods, and other probabilistic algorithms. In this context, a crucial scientific endeavour is to develop effective methods that allow the characterization of random number generators. However, commonly employed methods either lack formality (e.g. the NIST test suite), or are inapplicable in principle (e.g. the characterization derived from the Algorithmic Theory of Information (ATI)). In this letter we present a novel method based on Bayesian model selection, which is both rigorous and effective, for characterizing randomness in a bit sequence. We derive analytic expressions for a model's likelihood which is then used to compute its posterior probability distribution. Our method proves to be more rigorous than NIST's suite and the Borel-Normality criterion and its implementation is straightforward. We have applied our method to an experimental device based on the process of spontaneous parametric downconversion, implemented in our laboratory, to confirm that it behaves as a genuine quantum random number generator (QRNG). As our approach relies on Bayesian inference, which entails model generalizability, our scheme transcends individual sequence analysis, leading to a characterization of the source of the random sequences itself.Comment: 25 page

Análisis del juego de ataque en balonmano femenino

.- This study focuses on the specific organization of the attacking strategies in women's handball. In particular, we explore the specific weight of the two possible modalities of attack: positional and counterattack. To do so, during the 2008/2009 season, we have analyzed through a systematic observation methodology, direct and non-participant, the matches of a team that plays in the First Division of Women's Handball. To determine the rates of effectiveness, we have studied more than 2000 attacks and 900 throws on goal. Statistical analysis revealed that counterattack is more effective than positional play, and that it has a closer relationship with victory.Este estudio examinó la específica organización del juego de ataque en balonmano femenino. En concreto, hemos explorando el peso específico de los dos posibles tipos de ataque: posicional y contraataque. Para ello, hemos analizado los partidos de un mismo equipo de División de Honor Femenina durante la temporada 2008/2009 mediante metodología de la observación sistemática, directa y no participante. Hemos estudiado más de 2000 jugadas de ataque y 900 lanzamientos a portería, determinando de esta manera los índices de efectividad. El análisis estadístico reveló que existe una mayor eficacia del contraataque frente al juego posicional, además de una mayor relación con la victoria final

Ocean monitoring using GNSS-R techniques and microwave radiometry: The pau instrument concept

Peer Reviewe

Strategic planning for community sustainability in model forests: Case study of the Yoro model forest, Honduras

El estudio plantea una planificación estratégica de desarrollo en los Bosques Modelo a partir del estudio del caso del Bosque Modelo de Yoro, en Honduras, en donde el sector de la industria maderera y en concreto el subsector de carpintería y mueble, parece tener más ventajas competitivas para producir productos de exportación que generen riqueza en la zona, dada la escasa capacidad de compra de la región. A este subsector se le realiza un Análisis estratégico, una Elección estratégica y una Implementación estratégica determinando que el desarrollo del subsector podría pasar por crear una cooperativa capaz de suministrar partes de muebles a una empresa de carácter internacional que tenga como estrategia comercial la venta de muebles naturales, ecológicos y que esté comprometida socialment

El uso de señales de oportunidad GPS para observación de la Tierra

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New instrument concepts for ocean sensing: analysis of the PAU-radiometer

Sea surface salinity can be remotely measured by means of L-band microwave radiometry. However, the brightness temperature also depends on the sea surface temperature and on the sea state, which is probably today one of the driving factors in the salinity retrieval error budgets of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission and the NASA-Comision Nacional de Actividades Espaciales Aquarius/SAC-D mission. This paper describes the Passive Advanced Unit (PAU) for ocean monitoring. PAU combines in a single instrument three different sensors: an L-band radiometer with digital beamforming (DBF) (PAU-RAD) to measure the brightness temperature of the sea at different incidence angles simultaneously, a global positioning system (GPS) reflectometer [PAU-reflectometer of Global Navigation Satellite Signals (GNSS-R)] also with DBF to measure the sea state from the delay-Doppler maps, and two infrared radiometers to provide sea surface temperature estimates. The key characteristic of this instrument is that both PAU-RAD and the PAU-GNSS/R share completely the RF/IF front-end, and analog-to-digital converters. Since in order to track the GPS-reflected signal, it is not possible to chop the antenna signal as in a Dicke radiometer, a new radiometer topology has been devised which makes uses of two receiving chains and a correlator, which has the additional advantage that both PAU-RAD and PAU-GNSS/R can be operated continuously and simultaneously to perform the sea-state corrections of the brightness temperature. This paper presents the main characteristics of the different PAU subsystems, and analyzes in detail the PAU-radiometer concept.Peer Reviewe