Revealing Cortical Layers In Histological Brain Images With Self-Supervised Graph Convolutional Networks Applied To Cell-Graphs

Identifying cerebral cortex layers is crucial for comparative studies of the cytoarchitecture aiming at providing insights into the relations between brain structure and function across species. The absence of extensive annotated datasets typically limits the adoption of machine learning approaches, leading to the manual delineation of cortical layers by neuroanatomists. We introduce a self-supervised approach to detect layers in 2D Nissl-stained histological slices of the cerebral cortex. It starts with the segmentation of individual cells and the creation of an attributed cell-graph. A self-supervised graph convolutional network generates cell embeddings that encode morphological and structural traits of the cellular environment and are exploited by a community detection algorithm for the final layering. Our method, the first self-supervised of its kind with no spatial transcriptomics data involved, holds the potential to accelerate cytoarchitecture analyses, sidestepping annotation needs and advancing cross-species investigation

Ordinal Potential-based Player Rating

A two-player symmetric zero-sum game is transitive if for any pure strategies $x$, $y$, $z$, if $x$ is better than $y$, and $y$ is better than $z$, then $x$ is better than $z$. It was recently observed that the Elo rating fails at preserving transitive relations among strategies and therefore cannot correctly extract the transitive component of a game. Our first contribution is to show that the Elo rating actually does preserve transitivity when computed in the right space. Precisely, using a suitable invertible mapping $\varphi$, we first apply $\varphi$ to the game, then compute Elo ratings, then go back to the original space by applying $\varphi^{-1}$. We provide a characterization of transitive games as a weak variant of ordinal potential games with additively separable potential functions. Leveraging this insight, we introduce the concept of transitivity order, the minimum number of invertible mappings required to transform the payoff of a transitive game into (differences of) its potential function. The transitivity order is a tool to classify transitive games, with Elo games being an example of transitive games of order one. Most real-world games have both transitive and non-transitive (cyclic) components, and we use our analysis of transitivity to extract the transitive (potential) component of an arbitrary game. We link transitivity to the known concept of sign-rank: transitive games have sign-rank two; arbitrary games may have higher sign-rank. Using a neural network-based architecture, we learn a decomposition of an arbitrary game into transitive and cyclic components that prioritises capturing the sign pattern of the game. In particular, a transitive game always has just one component in its decomposition, the potential component. We provide a comprehensive evaluation of our methodology using both toy examples and empirical data from real-world games

Modelli della sensibilità allo strain-rate e identificazione dei parametri caratteristici di lamiere di acciaio

È ormai ampiamente riconosciuto che i materiali hanno un comportamento che varia con la velocità di deformazione. L'influenza della velocità sulle proprietà del materiale viene modellata tramite modelli costitutivi. I modelli che sono stati proposti sono numerosi e differenti fra di loro e non esistono dei criteri ben definiti per la loro scelta. I dati caratteristici dei vari materiali non sempre sono disponibili anche perché la loro identificazione è piuttosto difficoltosa. Scopo del lavoro è di implementare una procedura numerica per l'identificazione dei parametri di influenza rispetto alla velocità di deformazione, tramite la simulazione di una prova sperimentale. Per questo scopo sono stati considerati e confrontati diversi modelli. Di questi modelli si sono messi in evidenza i vantaggi e le principali limitazioni e si sono potuti determinare i parametri per i due materiali considerat

Consensus Multiplicative Weights Update: Learning to Learn using Projector-based Game Signatures

Cheung and Piliouras (2020) recently showed that two variants of the Multiplicative Weights Update method - OMWU and MWU - display opposite convergence properties depending on whether the game is zero-sum or cooperative. Inspired by this work and the recent literature on learning to optimize for single functions, we introduce a new framework for learning last-iterate convergence to Nash Equilibria in games, where the update rule's coefficients (learning rates) along a trajectory are learnt by a reinforcement learning policy that is conditioned on the nature of the game: \textit{the game signature}. We construct the latter using a new decomposition of two-player games into eight components corresponding to commutative projection operators, generalizing and unifying recent game concepts studied in the literature. We compare the performance of various update rules when their coefficients are learnt, and show that the RL policy is able to exploit the game signature across a wide range of game types. In doing so, we introduce CMWU, a new algorithm that extends consensus optimization to the constrained case, has local convergence guarantees for zero-sum bimatrix games, and show that it enjoys competitive performance on both zero-sum games with constant coefficients and across a spectrum of games when its coefficients are learnt

Effects of opioids on proximal renal tubular cells undergoing ATP depletion.

Abstract This study investigated the effect of morphine, fentanyl, butorphanol and buprenorphine on viability and caspase-3 activity in renal proximal tubular cells exposed to opioids for 2 h before or 12 h after chemical anoxia. Cell viability decreased regardless the treatment although intracellular ATP content was elevated in morphine and fentanyl pre-treated cells at 12 h. Anoxia increased caspase activity but this effect was significantly reduced in cells treated before or after with morphine, fentanyl and in cell treated with butorphanol for 12 h. No influence of buprenorphine was detected. Morphine, fentanyl and butorphanol might have protective effects during kidney ischemia

Educación y democracia: la construcción política en las instituciones educativas en perspectiva pedagógica

Ponencia presentada en el VIII Encuentro de Cátedras de Pedagogía de Universidades Nacionales Argentinas, realizado en La Plata del 8 al 10 de agosto de 2011. Fue publicada por la Facultad de Humanidades y Ciencias de la Educación de la Universidad Nacional de La Plata en el portal Web.La investigación se inscribe en las preocupaciones por comprender las relaciones entre lo político y lo pedagógico en Instituciones Educativas de Nivel Medio de la Provincia de Córdoba. Se propone reconocer representaciones y prácticas de ciudadanía democrática a través del decir de sus actores.¿Cómo se construye la democracia al interior de las instituciones educativas? ¿Cuándo y en cuáles prácticas –actos, hechos los actores institucionales reconocen prácticas democráticas? A través de un diseño cualitativo y de una investigación de tipo exploratoria y descriptiva se trabajará indagando y sistematizando los significados que los sujetos otorgan a sus prácticas en contextos institucionales singulares. Hipotetizamos que será posible identificar diversos (paradojales, heterogéneos, contradictorios) significados en la consideración con la que directivos y estudiantes definen y describen prácticas democráticas y que estos significados podrán encontrar algunas claves explicativas en las lógicas específicas de los diferentes niveles del sistema educativo, la singularidad de cada institución y su cultura institucional por un lado y en las relaciones intergeneracionales por otro. Se presentará una tipología con la identificación y clasificación provisorias de formas en que los estudiantes dan cuenta de las distintas maneras de habitar democráticamente los espacios educativos institucionales a partir de lo que entienden por experiencia democrática. El proyecto, que se realiza en forma interinstitucional entre la Universidad Nacional de Villa María y la Universidad Católica de Córdoba, fue aprobado en primera instancia por el Ministerio de Ciencia y Tecnología de la Provincia de Córdoba en la convocatoria PIO (proyectos de investigación orientados en ciencias sociales)