1,721,336 research outputs found
Bifurcation analysis of a physiological model of the baroreceptive control
No full textThe observation of biological systems suggests the hypothesis that nonlinear mechanisms could be involved in the control of their functions. The analysis of cardiovascular system, starting from the measurement of its state variables, seems to confirm the nonlinear nature of the control mechanisms and the presence of fractal structures in those signals. The goal of this study is to verify if a physiological control system is able to generate complex and also chaotic dynamics when periodically forced by a sinusoidal input at different frequencies. The paper analyzes a simple physiological model which accounts for the oscillations in the arterial blood pressure signal generated by the action of the baroreceptive control. The model was proposed by Kitney in 1979 and it considers the effect of the respiration signal like an external periodically forcing term. Using this model, a variety of nonlinear behaviors like the frequency entrainment, the phase locking and the frequency shift can be reproduced in different experimental situations. A study of the dynamics of the baroreceptive model through a structural stability analysis is proposed. The bifurcation diagrams classifies the different dynamical behavior of the model for different values of respiratory frequency and gain of baroreceptive system parameters. Other model parameters are fixed at realistic values. The large number of bifurcations of different types indicate that the dynamics of the model can be very complex. In fact, for values of parameters in physiological range, multiplicity of attractors, subharmonics of various periods, period doublings, quasiperiodic solutions and strange attractors get up. Results are in agreement with the hypothesis that a nonlinear dynamic model underlines the variability control
The “low tide” of tourist flows in the COVID-19 era. Insights into the economic and social shades of the ongoing phenomenon
No full textThe COVID-19 pandemic is an unprecedented global crisis. Many countries have implemented restrictions on population movement, instituting full or partial lockdowns in Spring 2020 as nowadays. The Coronavirus emergency has imposed the need to introduce restrictions that have also had a great impact on tourism. The interventions of the European Commission and the containment policies of the population adopted by different member States, as well as by those outside Europe, have resulted in the closure and crisis of the tourism sector in most of the destinations. What it can be observed it’s a sort of “low tide” of the tourist flows all around the world. Moving from these considerations, the paper aims at contributes to the debate on the binomial COVID-19 and tourism. After an introductory frame of the pandemic ongoing phenomenon, the paper focuses on the dynamics relating to the crucial sectors of air and cruise tourism, moving then to the analysis of the coastal and inland areas’ situation. The proposed analysis is developed through the consideration of three elements characterizing the current scenario: the relevance of the pandemic shock wave; the adaptability of companies and operators’ behaviour to changes and challenges; the unexpected and countertrend situation of arising positive externalities in some areas, such as the internal ones
Experimental setup for the quantification of the cardio pulmonary responses to different artificial respiratory loads
No full text
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
XVI Rapporto Territori in transizione. Geografie delle aree marginali tra permanenze e cambiamenti
No full textVariations 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
Nonlinearity parameters for the classification of high risk Myocardial Infarction subjects
No full textThe paper presents the analysis of the Heart Rate Variability (HRV) signal in 19 subjects who recently had a Myocardial Infarction episode (MI). The study follows a nonlinear approach based on the multiparametric analysis of some invariant properties of the dynamical system generating the time series. First we reconstruct the system embedding space from the HRV time series. The False Nearest Neighbors (FNN) criterion provides the real embedding dimension value. Results show that through the FNN method it is possible to identify the correct number of LE in the system. Parameter values significantly separate subjects who after MI keep a good performance of the cardiac pump (normal ventricular ejection function, NEF) vs. the group which after MI shows a reduced ventricular ejection fraction (REF)
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