Two distinct desynchronization processes caused by lesions in globally coupled neurons

To accomplish a task, the brain works like a synchronized neuronal network where all the involved neurons work together. When a lesion spreads in the brain, depending on its evolution, it can reach a significant portion of relevant area. As a consequence, a phase transition might occur: the neurons desynchronize and cannot perform a certain task anymore. Lesions are responsible for either disrupting the neuronal connections or, in some cases, for killing the neuron. In this work, we will use a simplified model of neuronal network to show that these two types of lesions cause different types of desynchronization.Comment: 5 pages, 3 figure

Satellite Altimetry and Current-Meter Velocities in the Malvinas Current at 41°S: Comparisons and Modes of Variations

Three year long current-meter arrays were deployed in the Malvinas Current at 418S below a satellite altimeter track at about 10 years intervals. Surface geostrophic velocities (SGV) derived from satel- lite altimetric data are compared with the in situ velocities at the upper current meter (􏰁300 m). Multisatel- lite gridded SGV compare better with in situ observations than along-track SGV. In spite of the proximity of the moorings to the complex Brazil-Malvinas Confluence (BMC) region, satellite SGV are significantly corre- lated with the 20 day low-passed in situ velocities (0.85 for along-isobaths velocities, 0.8 for cross-isobaths velocities). The recent in situ measurement period (2014?2015) stands out in the altimetry record with a long-lasting (4 months) high level of eddy kinetic energy at the mooring site and a southernmost location of the Subantarctic Front (SAF). The first two modes of variations of sea level anomaly (SLA) over the BMC remarkably match the first two modes of the low-passed in situ velocities. The first mode is associated with a latitudinal migration of the SAF, and the second with a longitudinal displacement of the Brazil Current overshoot. The two modes dominate the 24 year long record of SLA in the BMC, with energy peaks at the annual and semiannual periods for the first mode and at 3?5 months for the second mode. The SLA over the Southwest Atlantic was regressed onto the two confluence modes of SLA variations and showed remarkable standing wave train like structures in the Argentine Basin.Fil: Ferrari, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Artana, Camila Indira. Universite de Paris VI; FranciaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Provost, Christine. Universite de Paris VI; Franci

Phase synchronization of coupled bursting neurons and the generalized Kuramoto model

Bursting neurons fire rapid sequences of action potential spikes followed by a quiescent period. The basic dynamical mechanism of bursting is the slow currents that modulate a fast spiking activity caused by rapid ionic currents. Minimal models of bursting neurons must include both effects. We considered one of these models and its relation with a generalized Kuramoto model, thanks to the definition of a geometrical phase for bursting and a corresponding frequency. We considered neuronal networks with different connection topologies and investigated the transition from a non-synchronized to a partially phase-synchronized state as the coupling strength is varied. The numerically determined critical coupling strength value for this transition to occur is compared with theoretical results valid for the generalized Kuramoto model.Comment: 31 pages, 5 figure

Prediciendo con la regla de los signos de Descartes

En este reporte se discute, desde la socioepistemología, una experiencia realizada con estudiantes de bachillerato respecto de la Regla de los signos de Descartes, aquella que permite determinar el número de raíces positivas que una función polinómica podría presentar. El diseño de la secuencia de aprendizaje requirió el uso de la Ingeniería Didáctica como metodología, aunque no buscábamos validar la actividad de aprendizaje, sino analizar las herramientas que los estudiantes evocaran o construyeran en la experiencia

Testing statistical hypothesis on random trees and applications to the protein classification problem

Efficient automatic protein classification is of central importance in genomic annotation. As an independent way to check the reliability of the classification, we propose a statistical approach to test if two sets of protein domain sequences coming from two families of the Pfam database are significantly different. We model protein sequences as realizations of Variable Length Markov Chains (VLMC) and we use the context trees as a signature of each protein family. Our approach is based on a Kolmogorov--Smirnov-type goodness-of-fit test proposed by Balding et al. [Limit theorems for sequences of random trees (2008), DOI: 10.1007/s11749-008-0092-z]. The test statistic is a supremum over the space of trees of a function of the two samples; its computation grows, in principle, exponentially fast with the maximal number of nodes of the potential trees. We show how to transform this problem into a max-flow over a related graph which can be solved using a Ford--Fulkerson algorithm in polynomial time on that number. We apply the test to 10 randomly chosen protein domain families from the seed of Pfam-A database (high quality, manually curated families). The test shows that the distributions of context trees coming from different families are significantly different. We emphasize that this is a novel mathematical approach to validate the automatic clustering of sequences in any context. We also study the performance of the test via simulations on Galton--Watson related processes.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS218 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Agua potable: problemas en el abastecimiento de la ciudad de Bahía Blanca, Argentina

In April 2000, alterations in drinking water quality, such as turbidity and odors similar to those of organochloride pesticides, were detected at Bahía Blanca (Argentina). This fact was associated to reports of dermic reactions and respiratory problems in the population. Samples drawn from Paso de las Piedras reservoir, two water treatment plants of at inlet and outlet points and at several particular houses were analyzed. Total phytoplankton in the reservoir varied between 49440 and 84832 cells.ml-1, while dominant species was, Anabaena circinalis. Efficiency to remove microorganisms (ER) by the treatment plants considering cell number of total phytoplankton was analyzed. Bacteriological analysis, qualitative and quantitative studies of phytoplankton, pesticides, THM (trihalomethanes) and BTEX (benzene, toluene, ethylbenzene and xylene) analysis were carried out in samples of domestic supply and in the treatment plants. Even though samples were bacteriological potable, Anabaena circinalis and Microcystis aeruginosa algae were found at high concentrations in some cases. No pesticides were detected. THM and BTEX were below guideline values into recommendations for drinking water. Geosmin was responsible for detected odors. Besides, Copaene, another volatile metabolite, which on account in its structure could be considered a Geosmin precursor, was also detected. In Argentina, this was the first report of Cyanobacteria presence in drinking water.En abril de 2000, en Bahía Blanca (Argentina), se detectaron alteraciones en el agua de bebida, turbidez y olor semejante a “Gamexane”. Esto coincidió con la aparición de problemas dérmicos y respiratorios en la población. Para determinar el origen del problema, se analizaron muestras, tomadas en el embalse Paso de las Piedras, en las plantas potabilizadoras y en varios domicilios particulares. En el embalse, la densidad celular del fitoplancton, fluctuó entre 49440 y 84832 cél/ml-1, muy por encima de los valores de referencia. Anabaena circinalis en altas concentraciones fue la especie dominante (48320 - 84032 células por mililitro). Se cuantificó la eficiencia de las plantas de tratamiento (algas-entrada/algas-salida). Anabaena circinalis y Microcystis aeruginosa fueron encontradas a la entrada y a la salida de las plantas, indicando una baja eficiencia de las plantas de tratamiento. Para el agua domiciliaria, se realizaron estudios fitoplanctonicos; análisis bacteriológicos; presencia de plaguicidas, trihalometanos y BTEX. Si bien, bacteriológicamente el agua era potable, se encontraron Cyanobacteria en algunos casos en concentraciones muy altas. La presencia de pesticidas resultó negativa. La media de los THM y de los valores de BTEX resultaron menores a valores guías para agua potable. Se detectó la presencia de Geosmina, resultando el responsable del fuerte olor. Asimismo, se halló otro metabolito volátil, Copaene, que por su estructura pudiera llegar a considerarse precursor de la Geosmina. Este es el primer reporte de la presencia de cianobacterias en aguas de consumo humano en Argentina.Facultad de Ciencias Naturales y MuseoFacultad de Ciencias Exacta

Low-Noise Charge Preamplifier for Electrostatic Beam Position Monitoring Sensor at the ELENA Experiment

AbstractThe Extra Low ENergy Antiproton ring (ELENA) is a synchrotron under construction at CERN aimed to decelerate the antiprotons from the existing Antiproton Decelerator (AD) to an energy of 100 keV. The orbit measurement of the beam is accomplished by 20 electrostatic Beam Position Monitoring (BPM) sensors to measure complete orbits every 20ms with a resolution of 0.1mm for intensities in the range of 1-3×107 charges. For the conditioning of the pick-up signals from the BPMs a low-noise charge amplifier has been purposely designed and is under testing. The circuit must feature a bandwidth of 40MHz and an equivalent input voltage noise spectral density of 0.4 nV/√Hz for a sensor capacitance CS of about 26 pF. After amplification, the sum and difference signals are analogically derived and sent over 50 m cables to further blocks for digitalization and processing

THE EFFECT OF ELECTRICAL STIMULATION ON AGED SKELETAL MUSCLE REGENERATIVE POTENTIAL

Increasing age typically results in a decreased skeletal muscle regenerative capacity after injury, a decreased muscle mass and weakness, ultimately resulting in an increased likelihood for falls, susceptibility to recurrent injury, and a prolonged recovery. In response to injury, aged muscle displays a decreased capacity to regenerate damaged myofibers. Instead, the repair response is characterized by fibrotic accumulation, a response that has been attributed to dysfunction of the muscle stem cell (MuSC) population. MuSCs are a reserve cell population that plays a central role in dictating muscle regeneration. Muscle contractile activity, elicited by exercise or electrical stimulation, for example, has been suggested to be an important intervention to increase blood flow to the injury area and to promote the activation of muscle MuSCs. The purpose of this study is to test the hypothesis that neuromuscular electrical stimulation (Estim) inhibits activation of the muscle progenitor cell (MPC) fibrogenic molecular program to enhance skeletal muscle regeneration in aged animals. MPCs represent a heterogenous myogenic cell population, the majority of which are MuSCs. Our in vivo studies demonstrate that two weeks of Estim enhances myofiber regeneration and increases tetanic force recovery in aged muscles after an acute injury. In vitro, we find that improved muscle regeneration in aged muscle following the application of Estim is concomitant with a rejuvenated MPC phenotype. Our results further suggest that the beneficial effect of Estim on MPC regenerative potential may be mediated by up-regulation of the anti-aging protein, Klotho. Taken together, these data provide evidence that Estim is a safe and effective method and to improve functional recovery after an acute injury in aged muscle. It is anticipated that findings from this study will aid in the development of clinically relevant rehabilitation programs to enhance the muscle healing response in a geriatric population

El color del cristal: reflexiones sobre reflexionar en biología

Una invitación a participar de un espacio que se interroga sobre: “¿Por qué y a quién importa pensar a las ciencias de la vida desde o junto a la filosofía, la historia y la teoría social? A su vez, ¿interesa a estas disciplinas tener como referentes a las ciencias de la vida?”, opera sobre nosotros de tres formas. La primera (que por irrelevante para los demás y fundamental para nosotros queremos pasar rápido de ella) es la sincronicidad (que no es la sincronía): estamos trabajando en una línea similar, y la base del texto que sometemos a discusión crítica ya existía al recibir el convite. La segunda, que está expresada en las preguntas, es la noción de interdisciplina, la vocación, que es más que la voluntad, de perforar los muros que las aíslan, generando tribus mutuamente indiferentes, cuando no hostiles, entre sí. La tercera es que empezamos a sospechar (y por lo tanto, a creer) que las disciplinas ya han dado todo de sí, y que llega el momento que, como buena semilla, dejen de ser para empezar a ser algo diferente.Facultad de Ciencias Naturales y Muse

Hacia un Nuevo Enfoque en Evaluaciones de Desempeño para Equipos de Desarrollo de Software Ágil en Argentina.

La adopción de Metodologías Ágiles en desarrollo de software ha conllevado una serie de cambios en la dinámica y estructura de los equipos. El presente trabajo busca comprender cómo se vincula esa nueva realidad con las Herramientas de Evaluación de Desempeño y qué tienen estas últimas para aportarle a las empresas que producen aplicaciones o tercerizan servicios de programación. Se caracterizará la teoría sobre dichas herramientas, como también la propuesta de las Metodologías Ágiles y qué métricas se pueden recabar a través del proceso. Posteriormente, se presentarán los hallazgos de estudios de caso respecto a la interacción entre ambos aspectos. Por último, se presentarán recomendaciones que busquen guiar la implementación de Herramientas de Evaluación de desempeño y la práctica cotidiana de desarrollo siguiendo Metodologías Ágiles para optimizar su rendimiento