1,720,959 research outputs found
Modellazione e simulazione del comportamento EM di strutture biologiche
No full textatti della XXVII Riunione Annuale del Gruppo Nazionale di Coordinamento di Elettrotecnica, Bologna, 15-17 Giugno 2011
Sensitivity Analysis on the Temperature Dependence of a Neuronal Signal Duration
No full textThe results of a study concerning the dependence of the neuron signal duration on stress and environmental conditions are presented. A 2D Finite Element model, coupling the Hodgkin Huxley and the Maxwell equations in Electro Quasi-Static form, is employed to effectively describe the neuron membrane active behaviour. The sensitivity of the model to some input controllable parameters in terms of the duration of the Action Potential is analysed
Sensitivity Analysis on a FEM model for a neuronal soma subjected to different input conditions
No full textThe reproduction of the physiological behaviour of the axon of nervous cells by means of finite element models
No full textThis paper describes 3D Finite Element modelling solutions for a segment of a nervous cell axon, which take into account the non linear and time varying dynamics of the membrane surrounding it in order to reproduce its physiological behaviour, in terms of Action Potentials (AP) elicitation and its temperature dependence. The axial-symmetry of the system is exploited in order to conduct a more efficient analysis. A combination of the so called Hodgkin-Huxley equations modelling the dynamics of the membrane voltage-controlled ionic channels, together with the Maxwell equations in Electro Quasi-Static approximation, describing the electromagnetic behaviour of each medium, is tackled in a numerical procedure implemented in a commercial Finite Elements multiphysical environment. The usefulness of Finite Elements in order to have interesting quantitative responses (field shape and axon physiological behaviour) is investigated. Two different models are presented here. One exploits the typical thin layer approximation for the axon membrane, proving to be useful when the field solution inside the membrane domain is not a matter of interest. Its performances are compared with the other model, which is introduced in order to obtain a more realistic representation of the studied system: the axon membrane is here realized with a non-linear active medium (exploiting its equivalent electric conductivity) allowing the reproduction of the electric potential also inside the membrane. The passive electrotonic nature of the membrane and the elicitation of an AP in presence of different stimuli are computed and the results are in keeping with the predicted ones. Finally the AP temperature dependences and the propagation effect are reproduced by using the corresponding best numerical model, i.e. The coarse one without membrane for the temperature, the more detailed with membrane for the propagation, leading to a trade off between the computational effort and the objective of the analysis. The models open a wide range of applications and extensions in order to understand the true behaviour of a complete neuron
Influence of uncertain electrical properties on the conditions for the onset of electroporation in an eukaryotic cell
No full textA detailed numerical investigation concerning the influence on the electrical response of an eukaryotic cell model due to the variations of the conductivity and permittivity of the plasma and nuclear membranes is carried out by means of a vertex analysis. The dynamics of three cell performances, the voltages across the external and the nuclear membrane, and the pores density are analyzed by adopting a novel FEM-based model coupled with the nonlinear equation describing the electroporation (EP) phenomenon. The variations of the electrical and morphological performances, when the cell is stressed by a nonideal step input, are studied in three interesting regimes, i.e., at the nominal threshold for the onset of EP, and when the applied stress is over or under the EP threshold. The performed numerical analysis puts in evidence that, around the nominal EP threshold, uncertainties may lead to an indeterminate state of the plasma membrane, whereas the other two regimes remain well definite
Simulation of the effects of axon compression on the propagation of the action potential
No full textGoing 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
- …
