1,721,067 research outputs found
Modeling the CD8 T-cell Immune Response : Mathematical Analysis and Multiscale Models
No full textL'infection d'un organisme par un agent pathogène déclenche l'activation des lymphocytes T-CD8 et l'initiation de la réponse immunitaire. Il s'ensuit un programme complexe de prolifération et de différenciation des lymphocytes T-CD8, contrôlé par l'évolution de leur contenu moléculaire. Dans ce manuscrit, nous présentons deux modèles mathématiques de la réponse T-CD8. Le premier se présente comme une équation différentielle à impulsions grâce à laquelle nous étudions l'effet du partage inégal des protéines lors des divisions cellulaires sur la régulation de l'hétérogénéité moléculaire. Le second est un modèle à base d'agents couplant la description d'une population discrète de lymphocytes T-CD8 à celle du contenu moléculaire de ces derniers. Ce modèle s'avère capable de reproduire les différentes phases caractéristiques de la réponse T-CD8 aux échelle cellulaire et moléculaire. Ces deux travaux supportent l'hypothèse que la dynamique cellulaire observée in vivo est le reflet de l'hétérogénéité moléculaire qui structure la population de lymphocytes T-CD8Infection of an organism by a pathogen triggers the activation of the CD8 T-cells and the initiation of the immune response. The result is a complex program of proliferation and differentiation of the CD8 T-cells, controlled by the evolution of their molecular content. In this manuscript, we present two mathematical models of the CD8 T-cell response. The first one is presented as an impulsive differential equation by which we study the effect of unequal molecular partitioning at cell division on the regulation of molecular heterogeneity. The second one is an agent-based-model that couples the description of a discrete population of CD8 T-cells and that of their molecular content. This model can reproduce the different typical phases of the CD8 T-cell response at both the cellular and the molecular scales. These two studies support the hypothesis that the cell dynamics observed in vivo is a consequence of the molecular heterogeneity structuring the CD8 T-cell populatio
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
A review on local asymptotic stability analysis for mathematical models of hematopoiesis with delay and delay-dependent coefficients
Full text linkInternational audienceStability analysis of mathematical models of hematopoiesis (blood cell production process), described by differential equations with delay, needs to locate eigenvalues of characteristic equations that are usually exponential polynomial functions with delay-dependent coefficients. It is then more complicated than for ordinary differential equations to determine conditions for all roots to have negative real parts. We present, on three models of increasing complexity, the tools and method that can be used, with their advantages and their limitations. The method consists in the reduction of the problem to the localization of roots of a real function, these roots giving critical values of the delay for which stability possibly switches
Etude mathématique d'équations aux dérivées partielles hyperboliques modélisant les processus de régulation des cellules sanguines - Applications aux maladies hématologiques cycliques
No full textPrésident du jury : M. Michel Langlais (Professeur, Université Bordeaux II). Examinateurs : M. Mostafa Adimy (MCF HDR, Université de Pau), M. Mohamed Amara (Professeur, Université de Pau), M. Jacques Henry (Directeur de recherches INRIA, Université Bordeaux I), M. Benoît Perthame (Professeur, Ecole Normale Supérieure Paris), M. Vitaly Volpert (Directeur de recherches CNRS, Université Lyon 1). Rapporteurs : M. Benoît Perthame (Professeur, Ecole Normale Supérieure Paris), M. Vitaly Volpert (Directeur de recherches CNRS, Université Lyon 1), M. Glenn Webb (Professeur, Vanderbilt University, Nashville, USA).The events allowing production and continuous renewal of blood cells represent a series of complex processes, called haematopoiesis, taking place in the bone marrow. Haematopoiesis is based on a pool of haematopoietic stem cells, having unique capacities of differentiation (capacity to generate all blood cells types) and self renewal (capacity to generate a daugther cell identical to the mother cell). We performed a mathematical study of haematopoiesis based on nonlinear age and maturity structured models. It allowed to highlight the influence of hematopoietic stem cells on the entire blood cell population, these cells actively acting on the population stability. Through the study of models without maturity structure, reduced by integration to a system of differential equations with distributed delay, we obtained the existence of oscillating solutions and, throughout the study of a Hopf bifurcation, of periodic solutions with very long periods compared to the cell cycle duration. These oscillations are characteristic of some blood diseases, called periodic, such as chronic myelogenous leukaemia, one of the most widespread forms of leukaemia. Our work represents a contribution to the study of this disease. Lastly, we considered a haematopoiesis model taking into account the action of some factors, external to the bone marrow, acting on stem cells differentiation. We proved the existence of oscillating solutions which may describe some periodic hematological diseases.L'ensemble des événements permettant la fabrication et le renouvellement continu des cellules du sang représente une série de processus complexes, appelée hématopoïèse, ayant lieu dans la moelle osseuse. L'hématopoïèse repose sur une réserve de cellules souches, dites hématopoïétiques, possédant des capacités uniques de différenciation (capacité à générer l'ensemble des cellules du sang) et d'auto-renouvellement (capacité à générer une cellule fille identique à la cellule mère). Nous avons réalisé une étude mathématique de l'hématopoïèse à l'aide de modèles non-linéaires structurés en âge et maturité. Elle a permis de mettre en évidence l'influence des cellules souches hématopoïétiques sur la population totale de cellules du sang, ces cellules agissant activement sur la stabilité de la population. Par l'étude de modèles non structurés en maturité, réduits par intégration à un système d'équations différentielles avec retard distribué, nous avons mis en évidence l'existence de solutions oscillantes et, à travers l'étude d'une bifurcation de Hopf, de solutions périodiques, avec de très longues périodes en comparaison de la durée du cycle cellulaire. Ces oscillations sont caractéristiques de maladies du sang dites cycliques, dont la leucémie myéloïde chronique, une forme très répandue de leucémie. Notre travail représente une contribution à l'étude de cette maladie. Enfin, nous nous sommes intéressés à un modèle d'hématopoïèse prenant en compte l'action de facteurs extérieurs à la moelle osseuse qui agissent sur la différenciation des cellules souches. Nous avons établi l'existence de solutions oscillantes pouvant décrire certaines maladies hématologiques cycliques
Etude mathématique d'équations aux dérivées partielles hyperboliques modélisant les processus de régulation des cellules sanguines - Applications aux maladies hématologiques cycliques
No full textPrésident du jury : M. Michel Langlais (Professeur, Université Bordeaux II). Examinateurs : M. Mostafa Adimy (MCF HDR, Université de Pau), M. Mohamed Amara (Professeur, Université de Pau), M. Jacques Henry (Directeur de recherches INRIA, Université Bordeaux I), M. Benoît Perthame (Professeur, Ecole Normale Supérieure Paris), M. Vitaly Volpert (Directeur de recherches CNRS, Université Lyon 1). Rapporteurs : M. Benoît Perthame (Professeur, Ecole Normale Supérieure Paris), M. Vitaly Volpert (Directeur de recherches CNRS, Université Lyon 1), M. Glenn Webb (Professeur, Vanderbilt University, Nashville, USA).The events allowing production and continuous renewal of blood cells represent a series of complex processes, called haematopoiesis, taking place in the bone marrow. Haematopoiesis is based on a pool of haematopoietic stem cells, having unique capacities of differentiation (capacity to generate all blood cells types) and self renewal (capacity to generate a daugther cell identical to the mother cell). We performed a mathematical study of haematopoiesis based on nonlinear age and maturity structured models. It allowed to highlight the influence of hematopoietic stem cells on the entire blood cell population, these cells actively acting on the population stability. Through the study of models without maturity structure, reduced by integration to a system of differential equations with distributed delay, we obtained the existence of oscillating solutions and, throughout the study of a Hopf bifurcation, of periodic solutions with very long periods compared to the cell cycle duration. These oscillations are characteristic of some blood diseases, called periodic, such as chronic myelogenous leukaemia, one of the most widespread forms of leukaemia. Our work represents a contribution to the study of this disease. Lastly, we considered a haematopoiesis model taking into account the action of some factors, external to the bone marrow, acting on stem cells differentiation. We proved the existence of oscillating solutions which may describe some periodic hematological diseases.L'ensemble des événements permettant la fabrication et le renouvellement continu des cellules du sang représente une série de processus complexes, appelée hématopoïèse, ayant lieu dans la moelle osseuse. L'hématopoïèse repose sur une réserve de cellules souches, dites hématopoïétiques, possédant des capacités uniques de différenciation (capacité à générer l'ensemble des cellules du sang) et d'auto-renouvellement (capacité à générer une cellule fille identique à la cellule mère). Nous avons réalisé une étude mathématique de l'hématopoïèse à l'aide de modèles non-linéaires structurés en âge et maturité. Elle a permis de mettre en évidence l'influence des cellules souches hématopoïétiques sur la population totale de cellules du sang, ces cellules agissant activement sur la stabilité de la population. Par l'étude de modèles non structurés en maturité, réduits par intégration à un système d'équations différentielles avec retard distribué, nous avons mis en évidence l'existence de solutions oscillantes et, à travers l'étude d'une bifurcation de Hopf, de solutions périodiques, avec de très longues périodes en comparaison de la durée du cycle cellulaire. Ces oscillations sont caractéristiques de maladies du sang dites cycliques, dont la leucémie myéloïde chronique, une forme très répandue de leucémie. Notre travail représente une contribution à l'étude de cette maladie. Enfin, nous nous sommes intéressés à un modèle d'hématopoïèse prenant en compte l'action de facteurs extérieurs à la moelle osseuse qui agissent sur la différenciation des cellules souches. Nous avons établi l'existence de solutions oscillantes pouvant décrire certaines maladies hématologiques cycliques
A review on local asymptotic stability analysis for mathematical models of hematopoiesis with delay and delay-dependent coefficients
No full textInternational audienceStability analysis of mathematical models of hematopoiesis (blood cell production process), described by differential equations with delay, needs to locate eigenvalues of characteristic equations that are usually exponential polynomial functions with delay-dependent coefficients. It is then more complicated than for ordinary differential equations to determine conditions for all roots to have negative real parts. We present, on three models of increasing complexity, the tools and method that can be used, with their advantages and their limitations. The method consists in the reduction of the problem to the localization of roots of a real function, these roots giving critical values of the delay for which stability possibly switches
Global Asymptotic Stability and Hopf Bifurcation for a Blood Cell Production Model
No full textInternational audienceWe analyze the asymptotic stability of a nonlinear system of two differential equations with delay describing the dynamics of blood cell production. This process takes place in the bone marrow where stem cells differentiate throughout divisions in blood cells. Taking into account an explicit role of the total population of hematopoietic stem cells on the introduction of cells in cycle, we are lead to study a characteristic equation with delay-dependent coefficients. We determine a necessary and sufficient condition for the global stability of the first steady state of our model, which describes the population's dying out, and we obtain the existence of a Hopf bifurcation for the only nontrivial positive steady state, leading to the existence of periodic solutions. These latter are related to dynamical diseases affecting blood cells known for their cyclic nature
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