1,721,215 research outputs found
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
Direct and inverse problems for some integro-differential equations arising in biology
No full textLes phénomènes de croissance et de fragmentation jouent un rôle central dans de nombreux phénomènes biologiques. La première partie de ce manuscript concerne un modèle de l'activité électrique d'un réseau de neurones. Il s'agit d'une équation de croissance-fragmentation non linéaire. Grâce à une technique introduite par B. Perthame et L. Ryzhik, dans un cas particulier, nous quantifions des régimes dans lequels cette équation se relaxe avec un taux exponentiel. La deuxième et la troisième parties traitent de problèmes inverses. Le premier concerne l'équation de croissance-fragmentation ayant un noyau auto-similaire et le second un modèle de transduction olfactive. Après régularisations adéquates, ces deux problèmes reviennent à inverser des opérateurs intégraux dont les noyaux ont une structure auto-similaire. Grâce à la transformée de Mellin des inégalités de continuité et controlabilité de l'opérateur intégral sont établies. à partir de données expérimentales, ces études permettent d'estimer des paramètres importants des équations pour lesquels aucune mesure expérimentale directe n'est possible. La quatrième partie traite d'un modèle probabiliste de sénescence réplicative d'une lignée aléatoire de levures. En se basant sur des données expérimentales et des simulations numériques, le signal de sénescence est identifié et quantifié, et les sources de l'hétérogénéité des tailles des télomères sont analysées. Le modèle permet de mener une analyse complète de l'évolution des tailles des télomères.Growth and fragmentation phenomena play a central role in several biological phenomena. The first part of this thesis introduces a model of the electrical activity of a neural network. The equation involved is a non-linear growth-fragmentation equation. Thanks to a technique introduced by B. Perthame and L. Ryzhik, in a particular case, we are able to quantify regimes in which the equation has an exponential relaxation. The second and third part of this thesis both deal with inverse problems. The first one involves a growth-fragmentation equation with a self-similar kernel and the second one is a model of olfactive transduction. After regularization steps, these two problems come down to invert some integral operators whose kernels have a self-similar structure. Thanks to the use of the Mellin transform, some continuity and controllability inequalities are established. Using experimental data, these studies make it possible to estimate important parameters of the equations for which no direct experimental measurements can be obtained. The fourth part deals with a probabilistic model of replicative senescence of a random yeast lineage. Based on experimental data and numerical simulations, the senescence signal is identified and quantified, and the different sources of heterogeneity in the lengths of the telomeres are analyzed. This model allows us to completely analyze the evolution of the lengths of the telomeres
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
Parabolic equations in biology: growth, reaction, movement and diffusion
No full textThis book presents several fundamental questions in mathematical biology such as Turing instability, pattern formation, reaction-diffusion systems, invasion waves and Fokker-Planck equations. These are classical modeling tools for mathematical biology with applications to ecology and population dynamics, the neurosciences, enzymatic reactions, chemotaxis, invasion waves etc. The book presents these aspects from a mathematical perspective, with the aim of identifying those qualitative properties of the models that are relevant for biological applications. To do so, it uncovers the mechanisms at work behind Turing instability, pattern formation and invasion waves. This involves several mathematical tools, such as stability and instability analysis, blow-up in finite time, asymptotic methods and relative entropy properties. Given the content presented, the book is well suited as a textbook for master-level coursework
PDEs for neural networks with internal states
No full textIn the context of mathematical neuroscience, the Integrate and Fire model undoubtedly enjoys great fame and a vast literature. Yet, its peculiar mathematical structure makes the study of this equation challenging and always open-ended. The classical model consists of an equation that describes the dynamics of a network of neurons based on the membrane potential of the cells. A network can be interconnected with excitatory or inhibitory linkages or disconnected, in which case the equation will be linear. We are interested in the asymptotic behaviour of such networks in the linear case, where mathematical tools such as the relative entropy, the integral method and Harris theory have been useful in proving the convergence towards the steady state. In the first extension of the classical Integrate and Fire model we propose, we replace the punctual boundary condition with a non-local term, introducing a randomness parameter. For this new system, we prove long-time convergence via Harris theory and relative entropy with Poincaré inequality independent of the random parameter. Furthermore, we study the asymptotic convergence of the solutions of this model to those of the classical one. In the second extension, we deal with the incorporation of a variable for the adaptation current. First, we study the dynamics of this last variable alone, analysing the regularity of the stationary solution in dependence on the parameters and the asymptotic behaviour by means of the different methods of relative entropy with compactness argument and integral method. We then investigate the dynamics of the two-dimensional model through numerical simulations and we make comparison with a similar Fokker-Planck equation with partial diffusion and non-linearity. A number of numerical simulations accompany the study of each analysed model, allowing its theoretical results to be supported or anticipated.Dans le contexte des neurosciences mathématiques, le modèle Intègre et Tire jouit sans aucun doute d'une grande renommée et d'une vaste littérature. Cependant, sa structure mathématique particulière rend l'étude de cette équation difficile et toujours ouvert. Le modèle classique consiste en une équation qui décrit la dynamique d'un réseau neuronal en fonction du potentiel de membrane des cellules. Un réseau peut être interconnecté par des liens excitateurs ou inhibiteurs, ou déconnecté, auquel cas l'équation sera linéaire. Nous nous intéressons au comportement asymptotique de ces réseaux dans le cas linéaire, où des outils mathématiques tels que l'entropie relative, la méthode integrale et la théorie de Harris ont été utiles pour démontrer la convergence vers l'état stationnaire. Dans la première extension du modèle classique d'Intègre et Tire que nous proposons, nous remplaçons la condition au bord ponctuelle par un terme non local, en introduisant un paramètre aléatoire. Pour ce nouveau système, nous prouvons la convergence en temps long au moyen de la théorie de Harris et de l'entropie relative avec une inégalité de Poincaré indépendante du paramètre aléatoire. De plus, nous étudions la convergence asymptotique des solutions de ce modèle vers celles du modèle classique. Dans la deuxième extension, nous traitons de l'ajout d'une variable pour le courant d'adaptation. Nous étudions d'abord la dynamique de cette variable seule, en analysant la régularité de la solution stationnaire en fonction des paramètres et le comportement asymptotique à l'aide des différentes méthodes de l'entropie relative avec argument de compacité et de la méthode intégrale. Nous étudions ensuite la dynamique du modèle bidimensionnel au moyen de simulations numériques et nous proposons des comparaisons avec une équation de Fokker-Planck similaire avec diffusion partielle et non-linéarité. Un certain nombre de simulations numériques accompagnent l'étude de chaque modèle analysé, ce qui permet d'étayer ou d'anticiper les résultats théoriques.Nel contesto delle neuroscienze matematiche, il modello di Integrate and Fire gode indubbiamente di grande fama e di una vasta letteratura. Eppure, la sua peculiare struttura matematica rende lo studio di questa equazione stimolante e sempre aperto. Il modello classico consiste in un'equazione che descrive la dinamica di una rete di neuroni in funzione del potenziale di membrana delle cellule. Una rete può essere interconnessa con legami eccitatori o inibitori o disconnessa, nel qual caso l'equazione sarà lineare. Noi siamo interessati al comportamento asintotico di tali reti nel caso lineare, dove strumenti matematici come l'entropia relativa, il metodo integrale e la teoria di Harris si sono rivelati utili per dimostrare la convergenza verso lo stato stazionario. Nella prima estensione del modello classico di Integrate and Fire che proponiamo, sostituiamo la condizione al bordo puntuale con un termine non locale, inserendo un parametro di casualità. Per questo nuovo sistema, dimostriamo la convergenza allo stato stazionario tramite la teoria di Harris e dell'entropia relativa con disuguaglianza di Poincaré indipendente dal parametro casuale. Inoltre, studiamo la convergenza asintotica delle soluzioni di questo modello a quelle del classico. Nella seconda estensione ci occupiamo di incorporare una variabile per la corrente di adattazione. In primo luogo, studiamo la dinamica di quest'ultima variabile sola, analizzando la regolarità della soluzione stazionaria in dipendenza dai parametri e studiando il comportamento asintotico tramite i differenti metodi dell'entropia relativa con argomento di compattezza e metodo integrale. Indaghiamo poi la dinamica del modello bidimensionale tramite delle simulazioni numeriche e lo confrontiamo con un'equazione di Fokker-Planck similare con diffusione parziale e nonlinearità. Alcune simulazioni numeriche accompagnano lo studio di ogni modello analizzato, permettendo così di supportarne o anticiparne i risultati teorici
Models of living tissues, numerical simulations and immunotherapy of cancers
No full textNous étudions deux types de modèles couramment utilisés pour la représentation en temps et en espace des tumeurs: l’équation de Cahn-Hilliard pour les tissus vivants et le modèle de Keller-Segel. Les méthodes numériques que nous développons cherchent à représenter de manière précise et efficace ces équations tout en préservant leurs propriétés. Pour l'équation de Cahn-Hilliard, notre étude s’appuie sur une méthode de relaxation dont nous prouvons la convergence vers le modèle initial. Même si elles représentent mathématiquement des phénomènes physiques proches de ceux étudiés en dynamique des fluides, les équations utilisées pour les tissus vivants sont souvent différentes pour rendre compte du caractère actif des cellules. Les équations résultantes contiennent de nombreuses singularités et dégénérescences qui sont difficiles à analyser théoriquement et simuler numériquement de manière efficace. La méthode de relaxation a été introduite pour faciliter l’implémentation de nos schémas numériques; nous proposons ainsi des schémas numériques éléments finis simples à adapter dans les codes pré-existants. Afin de préserver les propriétés des équations continues lors des simulations numériques, nous proposons des schémas numériques basés sur la Méthode de Variable Auxiliaire. Sur la base de ces travaux numériques, nous présentons l’étude de deux phénomènes biologiques.We study two classes of mathematical models currently used for the modeling in time and space of tumors: the Cahn-Hilliard equation for living tissues and the Keller-Segel model. The numerical methods we propose aim to represent these equations efficiently and accurately while preserving their properties. For the Cahn-Hilliard equation, our study is based on a relaxation method for which we prove the convergence to the original model. Even though the physical effects modeled by these equations are close to the ones studied in fluid dynamics, the equations used to model living tissues are different in order to represent the active behavior of cells. The resulting equations contain numerous singularities and degeneracies, which result in technical difficulties to analyze and simulate them efficiently.Our relaxation method has been introduced to facilitate the implementation of our numerical schemes. Hence, we propose numerical schemes that are easy to implement in already existing finite element software. In order to preserve the properties of the equations during numerical simulations, we design numerical schemes based on the Scalar Auxiliary Variable method. Based on these numerical works, we present two studies of biological phenomena
- …
