1,721,064 research outputs found
Metodo di visualizzazione e caratterizzazione del sistema nervoso mediante colorazione combinata per impregnazione metallica ed immunoistochimica
No full textVisualization of neuronal elements is of fundamental importance in modern neuroscience. Golgi-Cox impregnation is a widely employed method that provides detailed information about morphological characteristics of neurons, but none regarding their neurochemical features. Immunocytochemical procedures, on the other hand, can provide a high degree of biochemical specificity but poorer morphological details, in particular if compared to Golgi-Cox impregnation. Hence, the combined use of these two approaches is highly desirable especially for confocal microscopists that can exploit the advantages of both methods simultaneously.
Here we show an innovative procedure of perfusion and fixation of brain tissue, that allows, by applying Golgi-Cox impregnation and immunofluorescence in the same histological section, to obtain high-quality histological material, with a very simple and inexpensive method.
This procedure is based on three simple fixation steps: 1) a paraformaldehyde perfusion followed by a standard post-fixation to stabilize the subsequent immunofluorescence reaction; 2) the classical Golgi-Cox impregnation and 3) an immunofluorescence reaction in previously impregnated material. This combination allows simultaneous visualization of i) the structural details (Golgi-Cox impregnated neurons), ii) the antigens’ characterization, iii) the anatomical interactions between discrete neuronal elements and iv) the 3D reconstruction and modeling. The method is easy to perform and can be reproducibly applied by small laboratories and expanded through the use of different antibodies. Overall, the method presented in this study offers an innovative and powerful approach to study the nervous system especially by using confocal microscopy
Analyse comparée du role des "espaces charnières" entre "Nord" et "Sud" dans la mobilité des hommes: les cas des Pouilles (Italie) et du Touat (Algérie)
No full textSur le parcours migratoire du Sud vers le Nord, il est des territoires nationaux que les individus traversent simplement parce qu’ils se trouvent sur leur route, il en est d’autres qui constituent une destination intermédiaire dans leurs “plans de mobilité”. Celle-ci ne relève pas du pur hasard, elle s’inscrit dans la stratégie de migration par étape qu’autorisent certains de ces territoires qui ont la caractéristique d’insérer le migrant voire de le solliciter, de polariser et de rediffuser les flux migratoires vers des espaces plus au nord.
On retrouve ces traits dans les Pouilles et le Touat qui, tout en étant très différenciés à la fois par les données du milieu (région méditerranéenne aux frontières des pays développés et région saharienne hyper-aride aux frontières des pays les moins pauvres) et par les données culturelles (l’un appartient au monde chrétien, l’autre au monde musulman), ont en commun de projeter le migrant dans le monde occidental.
Mettre au même niveau les Pouilles et le Touat n’est pas sans intérêt: le choix de ces deux régions ne diminue en rien la mise en parallèle des flux migratoires est-ouest et sud-nord. Justement, parce qu’il s’agit de contextes différents, la comparaison peut déboucher sur les aspects inédits du fonctionnement en espaces charnières de certains territoires face au phénomène contemporain de la mobilité migratoire internationale.
Dans cette comparaison, il ne sera pas question de rechercher des éléments identiques (on n’en trouverait pas) mais de repérer les "déterminants" socio-spatiaux de la "pérennisation" des courants migratoires classiques. Au stade actuel de nos recherches respectives sur ce thème de la mobilité migratoire internationale, nous ne disposons pas de toutes les données que nous aurions souhaité comparer. Lorsque la comparaison fait défaut l’analyse porte sur les éléments qui font fonctionner une région ou l’autre en “espace charnière”
HfO2-based resistive switching memory devices for neuromorphic computing
Full text linkHfO2-based resistive switching memory (RRAM) combines several outstanding properties, such as high scalability, fast switching speed, low power, compatibility with complementary metal-oxide-semiconductor technology, with possible high-density or three-dimensional integration. Therefore, today, HfO2 RRAMs have attracted a strong interest for applications in neuromorphic engineering, in particular for the development of artificial synapses in neural networks. This review provides an overview of the structure, the properties and the applications of HfO2-based RRAM in neuromorphic computing. Both widely investigated applications of nonvolatile devices and pioneering works about volatile devices are reviewed. The RRAM device is first introduced, describing the switching mechanisms associated to filamentary path of HfO2 defects such as oxygen vacancies. The RRAM programming algorithms are described for high-precision multilevel operation, analog weight update in synaptic applications and for exploiting the resistance dynamics of volatile devices. Finally, the neuromorphic applications are presented, illustrating both artificial neural networks with supervised training and with multilevel, binary or stochastic weights. Spiking neural networks are then presented for applications ranging from unsupervised training to spatio-temporal recognition. From this overview, HfO2-based RRAM appears as a mature technology for a broad range of neuromorphic computing systems
SHIP: a computational framework for simulating and validating novel technologies in hardware spiking neural networks
Full text linkInvestigations in the field of spiking neural networks (SNNs) encompass diverse, yet overlapping, scientific disciplines. Examples range from purely neuroscientific investigations, researches on computational aspects of neuroscience, or applicative-oriented studies aiming to improve SNNs performance or to develop artificial hardware counterparts. However, the simulation of SNNs is a complex task that can not be adequately addressed with a single platform applicable to all scenarios. The optimization of a simulation environment to meet specific metrics often entails compromises in other aspects. This computational challenge has led to an apparent dichotomy of approaches, with model-driven algorithms dedicated to the detailed simulation of biological networks, and data-driven algorithms designed for efficient processing of large input datasets. Nevertheless, material scientists, device physicists, and neuromorphic engineers who develop new technologies for spiking neuromorphic hardware solutions would find benefit in a simulation environment that borrows aspects from both approaches, thus facilitating modeling, analysis, and training of prospective SNN systems. This manuscript explores the numerical challenges deriving from the simulation of spiking neural networks, and introduces SHIP, Spiking (neural network) Hardware In PyTorch, a numerical tool that supports the investigation and/or validation of materials, devices, small circuit blocks within SNN architectures. SHIP facilitates the algorithmic definition of the models for the components of a network, the monitoring of states and output of the modeled systems, and the training of the synaptic weights of the network, by way of user-defined unsupervised learning rules or supervised training techniques derived from conventional machine learning. SHIP offers a valuable tool for researchers and developers in the field of hardware-based spiking neural networks, enabling efficient simulation and validation of novel technologies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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