1,720,982 research outputs found
Study of a long time behavior of some piecewise deterministic Markov processes
No full textL’objectif de cette thèse est d’étudier le comportement en temps long de certains processus de Markov déterministes par morceaux (PDMP) dont le flot suivi par la composante spatiale commute aléatoirement entre plusieurs flots possédant un unique équilibre attractif (éventuellement le même pour chaque flot). Nous donnerons dans un premier temps un exemple d’étude d’un tel processus construit dans le plan à partir de flots associés à des équations différentielles linéaires stables où il est déjà possible d’observer des comportements contre-intuitifs. La deuxième partie de ce manuscrit est dédiée à l’étude et la comparaison de deux modèles de compétition pour une ressource dans un environnement hétérogène. Le premier modèle est un modèle alétoire simulant l’hétérogénéité temporelle d’un environnement sur les espèces en compétition à l’aide d’un PDMP. Son étude utilise des outils maintenant classiques sur l’étude des PDMP. Le deuxième modèle est un modèle déterministe (présentant sous forme d’un système d’équations différentielles) modélisant l’impact de l’hétérogénéité spatiale d’un environnement sur ces mêmes espèces. Nous verrons que malgré leur nature très différente, le comportement en temps long de ces deux systèmes est relativement similaire et est essentiellement déterminé par le signe des taux d’invasion de chacune des espèces qui sont des quantités dépendant exclusivement des paramètres du système et modélisant la vitesse de croissance (ou de décroissance) de ces espèces lorsqu’elles sont au bord de l’extinction.The objective of this thesis is to study the long time behaviour of some piecewise deterministic Markov processes (PDMP). The flow followed by the spatial component of these processes switches randomly between several flow converging towards an equilibrium point (not necessarily the same for each flow). We will first give an example of such a process built in the plan from two linear stable differential equations and we will see that its stability depends strongly on the switching times. The second part of this thesis is dedicated to the study and comparison of two competition models in a heterogeneous environment. The first model is a probabilistic model where we build a PDMP simulating the effect of the temporal heterogeneity of an environment over the species in competition. Its study uses classical tools in this field. The second model is a deterministic model simulating the effect of the spatial heterogeneity of an environment over the same species. Despite the fact that the nature of the two models is very different, we will see that their long time behavior is very similar. We define for both model several quantities called invasion rates modelizing the growth (or decreasing) rate speed of a species when it is near to extinction and we will see that the signs of these invasion rates fully describes the long time behavior for both systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Hétérogénéité spatiale en dynamique des populations
No full textThe purpose of this thesis is the mathematical and numerical study of a system of several species competing for a single resource in a heterogeneous environment. When the environment is homogeneous, it is known that such a system, called chemostat system, satisfies the so-called competitive exclusion principle: no more than one species can survive. We propose two spatially structured models and study the role of spatial heterogeneity in the coexistence phenomena. The first model is a system of matrix equations, the second one is a reaction-diffusion system. Our first contribution is to show that the solutions of the reaction-diffusion system are uniformly bounded in time and space in L infinity norm. Next, we study the case of small migration rate in the discrete model and show that the coexistence of several species is possible. Lastly, in the case of high migration rates, we use the center manifold theorem to show in each of the two models that the principle of competitive exclusion holds. Then, we construct stationary coexistence solutions for two species using a method of global bifurcations. This construction leads to the identification of a coexistence domain in the parameter space. In the final chapters, we illustrate and extend numerically the previous results. In particular, we show how the coexistence domain depends on the migration rate and on the spatial heterogeneity.L'objet de cette thèse est l'étude mathématique et numérique d'un système de compétition de plusieurs espèces pour une ressource dans un milieu hétérogène. Lorsque le milieu est homogène, il est connu qu'un tel système, appelé système de chemostat, vérifie le principe d'exclusion compétitive : au plus une espèce peut survivre. Nous proposons deux modèles spatialement structurés et étudions le rôle de l'hétérogénéité spatiale dans les phénomènes de coexistence. Le premier modèle est un système d'équations matricielles et le second un système de réaction-diffusion. Notre première contribution est de montrer que les solutions du système de réaction-diffusion sont uniformément bornées en temps et en espace en norme L infini. Nous étudions ensuite le cas des petits taux de migration dans le modèle discret et montrons que la coexistence est possible. Dans le cas des grands taux de migration, nous montrons à l'aide du théorème de la variété centrale que pour chacun des deux modèles, le principe d'exclusion compétitive est vérifié. Nous construisons finalement des solutions stationnaires de coexistence pour deux espèces à l'aide d'une méthode de bifurcations globales. Cette construction nous amène à définir la notion de domaine de coexistence dans l'espace des paramètres. Dans les derniers chapitres, nous illustrons et étendons numériquement les résultats précédents. Nous montrons en particulier comment le domaine de coexistence dépend du taux de migration et de l'hétérogénéité spatiale
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