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1.
Neural Netw ; 71: 159-71, 2015 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-26356599

RESUMEN

A challenging problem when studying a dynamical system is to find the interdependencies among its individual components. Several algorithms have been proposed to detect directed dynamical influences between time series. Two of the most used approaches are a model-free one (transfer entropy) and a model-based one (Granger causality). Several pitfalls are related to the presence or absence of assumptions in modeling the relevant features of the data. We tried to overcome those pitfalls using a neural network approach in which a model is built without any a priori assumptions. In this sense this method can be seen as a bridge between model-free and model-based approaches. The experiments performed will show that the method presented in this work can detect the correct dynamical information flows occurring in a system of time series. Additionally we adopt a non-uniform embedding framework according to which only the past states that actually help the prediction are entered into the model, improving the prediction and avoiding the risk of overfitting. This method also leads to a further improvement with respect to traditional Granger causality approaches when redundant variables (i.e. variables sharing the same information about the future of the system) are involved. Neural networks are also able to recognize dynamics in data sets completely different from the ones used during the training phase.


Asunto(s)
Causalidad , Redes Neurales de la Computación , Algoritmos , Clasificación , Simulación por Computador , Entropía , Modelos Teóricos
2.
Acta Obstet Gynecol Scand ; 92(4): 457-60, 2013 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-23347183

RESUMEN

Placenta accreta is a rare and potentially life-threatening complication of pregnancy characterized by abnormal adherence of the placenta to the uterine wall. A previously scarred uterus or an abnormal site of placentation in the lower segment is a major risk factor. The aim of this study was to investigate the change in the incidence of placenta accreta and associated risk factors along four decades, from the 1970s to 2000s, in a tertiary south Italian center. We analyzed all cases of placenta accreta in a sample triennium for each decade. The incidence increased from 0.12% during the 1970s, to 0.31% during the 2000s. During the same period, cesarean section rates increased from 17 to 64%. Prior cesarean section was the only risk factor showing a significant concomitant rise. Our results reinforce cesarean section as the most significant predisposing condition for placenta accreta.


Asunto(s)
Cesárea/estadística & datos numéricos , Placenta Accreta/epidemiología , Placenta Accreta/cirugía , Resultado del Embarazo/epidemiología , Salud de la Mujer , Adulto , Femenino , Humanos , Histerectomía/estadística & datos numéricos , Incidencia , Italia , Registros Médicos , Hemorragia Posparto/prevención & control , Embarazo , Factores de Riesgo , Adulto Joven
3.
Biol Cybern ; 103(6): 471-85, 2010 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-21165746

RESUMEN

Typical patterns of hand-joint covariation arising in the context of grasping actions enable one to provide simplified descriptions of these actions in terms of small sets of hand-joint parameters. The computational model of mirror mechanisms introduced here hypothesizes that mirror neurons are crucially involved in coding and making this simplified motor information available for both action recognition and control processes. In particular, grasping action recognition processes are modeled in terms of a visuo-motor loop enabling one to make iterated use of mirror-coded motor information. In simulation experiments concerning the classification of reach-to-grasp actions, mirror-coded information was found to simplify the processing of visual inputs and to improve action recognition results with respect to recognition procedures that are solely based on visual processing. The visuo-motor loop involved in action recognition is a distinctive feature of this model which is coherent with the direct matching hypothesis. Moreover, the visuo-motor loop sets the model introduced here apart from those computational models that identify mirror neuron activity in action observation with the final outcome of computational processes unidirectionally flowing from sensory (and usually visual) to motor systems.


Asunto(s)
Simulación por Computador , Neuronas Motoras/fisiología , Células Receptoras Sensoriales/fisiología , Humanos
4.
Brain Res ; 1225: 133-45, 2008 Aug 15.
Artículo en Inglés | MEDLINE | ID: mdl-18538746

RESUMEN

This paper addresses the problem of extracting view-invariant visual features for the recognition of object-directed actions and introduces a computational model of how these visual features are processed in the brain. In particular, in the test-bed setting of reach-to-grasp actions, grip aperture is identified as a good candidate for inclusion into a parsimonious set of hand high-level features describing overall hand movement during reach-to-grasp actions. The computational model NeGOI (neural network architecture for measuring grip aperture in an observer-independent way) for extracting grip aperture in a view-independent fashion was developed on the basis of functional hypotheses about cortical areas that are involved in visual processing. An assumption built into NeGOI is that grip aperture can be measured from the superposition of a small number of prototypical hand shapes corresponding to predefined grip-aperture sizes. The key idea underlying the NeGOI model is to introduce view-independent units (VIP units) that are selective for prototypical hand shapes, and to integrate the output of VIP units in order to compute grip aperture. The distinguishing traits of the NEGOI architecture are discussed together with results of tests concerning its view-independence and grip-aperture recognition properties. The overall functional organization of NEGOI model is shown to be coherent with current functional models of the ventral visual stream, up to and including temporal area STS. Finally, the functional role of the NeGOI model is examined from the perspective of a biologically plausible architecture which provides a parsimonious set of high-level and view-independent visual features as input to mirror systems.


Asunto(s)
Encéfalo/fisiología , Fuerza de la Mano/fisiología , Mano/fisiología , Percepción de Movimiento/fisiología , Reconocimiento Visual de Modelos/fisiología , Desempeño Psicomotor/fisiología , Algoritmos , Simulación por Computador , Dedos/fisiología , Humanos , Red Nerviosa/fisiología , Redes Neurales de la Computación
5.
Maturitas ; 43(4): 277-81, 2002 Dec 10.
Artículo en Inglés | MEDLINE | ID: mdl-12468136

RESUMEN

OBJECTIVE: To assess the efficacy of dexketoprofen (DEX) in reducing pain at different stages of the hysteroscopic procedure in comparison with local anaesthesia in menopausal women. METHODS: Menopausal patients affected by uterine bleeding submitted to diagnostic hysteroscopy, were randomised to receive either 25 mg DEX tablet (n = 148) or intracervical injection of 5 ml mepivacaine 2% (n = 150). Pain suffered during the procedure itself and 30, 60, 120 min after, was scored on the 11 point Visual Analogic Scale, recorded and analysed. RESULTS: No statistical difference were noted during the procedure itself in both groups of treatment. Patients treated with DEX has significantly less postoperative pain. CONCLUSIONS: DEX is not superior to mepivacaine in reducing the discomfort of the procedure but does significantly reduce postoperative pain.


Asunto(s)
Antiinflamatorios no Esteroideos/uso terapéutico , Cetoprofeno/análogos & derivados , Cetoprofeno/uso terapéutico , Dolor Postoperatorio/tratamiento farmacológico , Trometamina/análogos & derivados , Trometamina/uso terapéutico , Administración Oral , Antiinflamatorios no Esteroideos/administración & dosificación , Femenino , Humanos , Histeroscopía , Inyecciones , Cetoprofeno/administración & dosificación , Mepivacaína/administración & dosificación , Mepivacaína/uso terapéutico , Dimensión del Dolor , Posmenopausia , Resultado del Tratamiento , Trometamina/administración & dosificación
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